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95 2d affi" } COMMITTEE PRINT 


Prepared at the Keqtiest of 
Hon. Howard W. Cannon, Chairman 

Printed for the use of the 
Committee on Commerce, Science, and Transportation 



2d Session J 



Prepared at the Request of 

Hox. Howard W. Cannon, Chairman 


MAY 1978 

Printed for the use of the 
Committee on Commerce, Science, and Transportation 

U.S. government printing office 

34-857 WASHINGTON : 1978 


HOWARD W. CANNON, Nevada, Chairman 

RUSSELL B. LONG, Louisiana 
ERNEST F. HOLLINGS, South Carolina 
WENDELL H. FORD, Kentucky 
JOHN A. DURKIN, New Hampshire 
DONALD W. RIEGLE, Jr., Michigan 

Aubrey L. Sarvis, Staff Director and Chief Counsel 

Edwin K. Hall, General Counsel 
Malcolm M. B. Sterrett, Minority Staff Director 



U.S. Senate, 

Committee on Commerce, Science, and Transportation, 

November 15, 1978. 
To the members of the Committee on Commerce. Science, and 
Transportation, U.S. Senate: 

I am pleased to transmit herewith for your information and use the 
following report on "Weather Modification: Programs, Problems, 
Policy, and Potential." 

The report was prepared at my request by the Congressional Re- 
search Service under the direction of Dr. Robert Morrison, Specialist 
in Earth Sciences, Science Policy Research Division. We thank Dr. 
Morrison and the others involved in the study for their extremely 
thorough and scholarly report. Substantial material on almost all 
areas of weather modification are included and the report will provide 
the committee with an excellent reference source for future delibera- 
tions on the subject. 

The completion of the report is particularly timely due to the up- 
coming recommendations expected from the Weather Modification 
Advisory Board and the Department of Commerce (as directed by 
Public Law 94-490) on the future Federal role in weather 

James B. Pearson, 
Ranking minority member. 



U.S. Senate, 

Committee on Commerce, Science, and Transportation, 

Washington, D.C., July 30, 1976. 

Dr. Norman A. Beckman, 

Acting Director, Congressional Research Service, 
Library of Congress, W ashington, D.C. 

Dear Dr. Beckman: Weather modification, although a relatively 
young science, has over the years stimulated great interest within the 
scientific, commercial, governmental, and agricultural communities. 
Such responses are readily understandable. Weather-related disasters 
and hazards affect virtually all Americans and annually cause untold 
human suffering and loss of life and result in billions of dollars of eco- 
nomic loss to crops and other property. While weather modification 
projects have been operational for nearly 25 years and have been 
shown to have significant potential for preventing, diverting, moderat- 
ing, or ameliorating the adverse effects of such weather related disas- 
ters and hazards, I am greatly concerned regarding the lack of a 
coordinated Federal weather modification policy and a coordinated 
and comprehensive program for weather modification research and 
development. This fact is all the more disturbing in view of the mani- 
fest needs, and benefits, social and economic, that can be associated with 
weather modification activities. These deficiencies in our Federal orga- 
nizational structure have resulted in a less than optimal return on our 
investments in weather modification activities and a failure, with few 
exceptions, to recognize that much additional research and develop- 
ment needs to be carried out before weather modification becomes a 
truly operational tool. 

Reports and studies conducted by such diverse organizations as the 
National Academy of Sciences, the National Advisory Committee on 
Oceans and Atmosphere, the General Accounting Office, and the 
Domestic Council have highlighted the lack of a comprehensive Federal 
weather modification policy and research and development program. 
Hearings that I chaired in February of this year reinforced my con- 
cerns regarding the wisdom of our continued failure to implement a 
national policy on this very important issue. 

I am therefore requesting the Congressional Research Service to 
prepare a comprehensive report on weather modification. This report 
should include a review of the history and existing status of weather 
modification knowledge and technology; the legislative history of 
existing and proposed domestic legislation concerning weather mod- 
ification; socio-economic and legal problems presented by weather 
modification activities; a review and analysis of the existing local, 
State, Federal, and international weather modification organizational 



structure: international implications of weather modification activi- 
ties: and a review and discussion of alternative U.S. and international 
weather modification policies and research and development programs. 

If you have any questions with respect to this request, please contact 
Mr. Gerry J. Kovach, Minority Staff Counsel of the Senate Commerce 
Committee. He has discussed this study with Mr. Robert E. Morrison 
and Mr. John Justus of the Science Policy Division, Congressional 
Research Service. 

Very truly yours, 

James B. Pearsox, 

U.S. Senator. 


The Library of Congress, 
congressional research service, 

Washington, D.C., June 19, 1978. 

Hon. James B. Pearson, 

Committee on Commerce, Science, and Transportation, 
U.S. Senate, Washington, D.C. 

Dear Senator Pearson: The enclosed report, entitled "Weather 
Modification: Programs, Problems, Policy, and Potential," has been 
prepared by the Congressional Research Service in response to your 

The study reviews the history, technology, activities, and a number 
of special aspects of the field of weather modification. Activities 
discussed are those of the Federal, State, and local governments, of 
private organizations, and of foreign nations. Consideration is given 
to international, legal, economic, and ecological aspects. There are 
also an introductory chapter which includes a summary of issues, a 
chapter discussing inadvertent weather and climate modification, and 
a chapter summarizing recommendations from major Federal policy 

The study has been coordinated by Dr. Robert E. Morrison, Special- 
ist in Earth Sciences, Science Policy Research Division, who also 
prepared chapters 1, 2, 3, 5, 7, 8, and 9 as well as the Summary and 
Conclusions. Mr. John R. Justus, Analyst in Earth Sciences, and 
Dr. James E. Mielke, Analyst in Marine and Earth Sciences, both 
of the Science Policy Research Division, contributed chapters 4 and 
6, respectively. Chapter 10 was prepared by Mrs. Lois B. McHugh, 
Foreign Affairs Analyst, Foreign Affairs and National Defense Di- 
vision. Chapter 11 was written jointly by Mrs. Nancy Lee Jones, 
Legislative Attorney, and Mr. Daniel Hill Zaf ren, Specialist in Ameri- 
can Public Law, both of the American Law Division. Dr. Warren 
Viessman, Jr., Senior Specialist in Engineering and Public Works, 
contributed chapter 12; and Mr. William C. JolW, Analyst in En- 
vironmental Policy, Environment and Natural Resources Division, 
was responsible for chapter 13. In addition, appendixes C, F, Q, and R 
were assembled by Mrs. McHugh ; appendixes D and S were prepared 
by Mrs. Jones; and information in the remaining appendixes was 
collected by Dr. Morrison. 

I trust that this report will serve the needs of the Committee on 
Commerce, Science, and Transportation as well as those of other 
committees and individual Members of Congress who are concerned 
with weather modification. On behalf of the Congressional Research 
Service, I wish to express my appreciation for the opportunity to 
undertake this timely and worthwhile assignment. 

Gilbert Gtjde, 



Digitized by the Internet Archive 
in 2013 



Letter of transmittal in 

Letter requesting study v 

Letter of submittal vn 

Summary and conclusions xix 

Chapter 1 

Introduction and summary of issues 1 

Perspective 1 

Situation 1 

Advantages 3 

Timeliness 5 

Definitions and scope of report 7 

Summary of issues in planned weather modification 9 

Technological problems and issues 9 

Governmental issues 12 

The role of the Federal Government 12 

Roles of State and local governments 14 

Legal issues 15 

Private rights in the clouds 15 

Liability for weather modification 16 

Interstate legal issues 17 

International legal issues 17 

Economic issues 18 

Issues complicating economic analyses of weather modifica- 
tion 18 

Weather modification and conflicting interests 19 

Social issues 19 

Social factors 20 

Need for public education on weather modification 21 

Decisionmaking 22 

International issues 23 

Ecological issues 24 

Chapter 2 

History of weather modification 25 

Introduction 25 

History of weather modification prior to 1946 26 

Prescientific period 26 

Early scientific period 27 

Development of scientific fundamentals 32 

Early cloud-seeding experiments 34 

Weather modification since 1946 35 

Chronology 35 

Langmuir, Schaefer, and Vonnegut 37 

Research projects since 1947 39 

Project Cirrus 39 

The Weather Bureau cloud phvsics project 41 

The U.S. experiments of 1953-54 42 

Arizona Mountain cumulus experiments 44 

Project Whitetop 44 

Climax experiments 45 

Lightning suppression experiments 46 

Fog dispersal research 46 

Hurricane modification. 46 

Hail suppression 46 

Foreign weather modification research 47 

Commercial operations 48 

History of Federal activities, committees, policy studies, and 

reports 53 



Chapter 3 


Technology of planned weather modification 55 

Introduction 55 

Assessment of the status of weather modification technology 56 

Classification of weather modification technologies 61 

Principles and status of weather modification technologies 62 

Precipitation augmentation 64 

Cumulus clouds 66 

Cumulus modification experiments 67 

Effectiveness of precipitation enhancement research and 

operations 69 

Results achieved through cumulus modification 70 

Recent advances in cumulus cloud modification 71 

Orographic clouds and precipitation 71 

Orographic precipitation modification 75 

Orographic seeding experiments and seedability criteria 77 

Operational orographic seeding projects 81 

Results achieved through orographic precipitation modifi- 
cation 82 

Hail suppression 84 

The hail problem 84 

Modification of hail 86 

Hail seeding technologies 87 

Evaluation of hail suppression technology 88 

Surveys of hail suppression effectiveness 89 

Conclusions from the TASH study 91 

Dissipation of fog and stratus clouds 92 

Cold fog modification 93 

Warm fog modification 93 

Lightning suppression 96 

Lightning modification 98 

Evaluation of lightning suppression technology 99 

Modification of severe storms 101 

Hurricanes 101 

Generation and characteristics of hurricanes 104 

Modification of hurricanes 108 

Tornadoes 112 

Modification of tornadoes 113 

Technical problem areas in planned weather modification 115 

Seeding technology 115 

Evaluation of weather modification projects 118 

Extended area effects of weather modification 124 

Approaches to weather modification other than seeding 129 

Research needs for the development of planned weather modification- 131 

General considerations 131 

Recommendations from the 1973 National Academv of Sciences 

study i 134 

Recommendations of the Advanced Planning Group of NOAA__. 136 

Summary of Federal research needs expressed by State officials. 138 
Research recommendations of the AMS Committee on Weather 

Modification 139 

Research recommendations related to extended area and time 

effects 143 

Chapter 4 

Inadvertent weather and climate modification 145 

Introduction 145 

Terminology 145 

Climate 145 

Climatic fluctuation and climatic change 146 

Weather 146 

Weather modification 146 

Climate modification 146 

Planned climate modification 147 

Inadvertent climate modification 148 



Background 149 

Historical perspective 149 

Understanding the causes of climatic change and variability 151 

The concept of climatic change and variability 152 

When and how do climatic changes occur 154 

The facts about inadvertent weather and climate modification 156 

Airborne particulate matter and atmospheric turbidity 156 

Do more particles mean a warming or cooling? 157 

Sources of atmospheric particulates: Natural vs. manmade.. 158 

Atmospheric processes affected by particulates 159 

The La Porte weather anomaly: Urban climate modification. 162 

Carbon dioxide and water vapor 164 

Increases in atmospheric carbon dioxide concentration: 

What the record indicates 164 

Predicting future atmospheric carbon dioxide levels 166 

Sources and sinks for carbon dioxide 168 

Atmospheric effects of increased carbon dioxide levels 169 

Implications of increasing atmospheric carbon dioxide con- 
centrations 169 

Implications of a climatic warming 170 

Carbon dioxide and future climate: The real climate vs. 

"model climate" 171 

Ozone depletion 172 

Concerns regarding ozone destruction 172 

Action by the Government on the regulation of fluorocar- 

bons 175 

Climatic effects of ozone depletion 176 

Waste heat 177 

The urban "Heat Island" 177 

Albedo 179 

Large-scale irrigation 180 

Recapitulation 181 

Issues in inadvertent weather and climate modification 184 

Climatic barriers to long-term energy growth 184 

Thoughts and reflections — Can we contemplate a fossil-fuel-free 

world? 185 

Research needs and deficiencies 186 

Chapter 5 

Federal activities in weather modification 193 

Overview of Federal activities..-- '— — 193 

Legislative and congressional activities 194 

Federal legislation on weather modification 194 

Summary 194 

The Advisory Committee on Weather Control 195 

Direction to the National Science Foundation 196 

Reporting of weather modification activities to the Federal 

Government 197 

The National Weather Modification Policy Act of 1976 198 

Congressional direction to the Bureau of Reclamation 201 

Proposed Federal legislation on weather modification 203 

Summary 203 

Legislation proposed in the 94th Congress and the 95th 

Congress, 1st sessions 205 

Other congressional activities 207 

Resolutions on weather modification 207 

Hearings 208 

Studies and reports by congressional support agencies 209 

Activities of the executive branch 209 

Introduction 209 

Institutional structure of the Federal weather modification 

program 210 

Current status of Federal organization for weather modifica- 
tion 210 



Federal structure; 1946-57 214 

Federal structure; 1958-68 215 

Federal structure; 1968-77 216 

Future Federal organization for weather modification 216 

Coordination and advisory mechanisms for Federal weather 

modification programs 221 

Introduction 221 

The Interdepartmental Committee for Atmospheric Sciences 

(ICAS) 222 

The National Academv of Sciences/Committee on At- 
mospheric Sciences (N AS/CAS) 226 

The National Advisory Committee on Oceans and Atmos- 
phere (NACOA) 227 

Other coordination and advisory mechanisms 228 

Weather Modification Advisory Board 231 

Weather modification activities reporting program 232 

Background and regulations 232 

Reporting of Federal activities 233 

Summary reports on U.S. weather modification activities 233 

Federal studies and reports on weather modification 234 

Introduction 234 

Studies of the early 1950's 235 

Advisory Committee on Weather Control 236 

National Academy of Sciences studies 237 

Studies bv the Interdepartmental Committee for Atmos- 
pheric Sciences (ICAS) 238 

Domestic Council study 239 

Policy and planning reports produced by Federal agencies 239 

Federal programs in weather modification 241 

Introduction and funding summaries 241 

Department of the Interior 246 

Introduction 246 

Project Skywater; general discussion 247 

The Colorado River Basin Pilot Project (CRBPP) 254 

The High Plains Cooperative Program (HIPLFX) 258 

The Sierra Cooperative Pilot Project (SCPP) 263 

Drought mitigation assistance 266 

National Science Foundation 267 

Introduction and general 267 

Weather hazard mitigation 274 

Weather modification technology development 282 

Inadvertent weather modification 283 

Societal utilization activities 287 

Agricultural weather modification 288 

Department of Commerce 290 

Introduction and general discussion 290 

The Florida Area Cumulus Experiment (FACE) 292 

Project Stormfurv 296 

Research Facilities Center (RFC) 300 

Global Monitoring for Climatic Change (GMCC) 301 

Lightning suppression 302 

Modification of extratropical severe storms 302 

Department of Defense 303 

Introduction 303 

Air Force fog dispersal operations 303 

Army research and development 304 

Navy research and development 304 

Air Force research and development 305 

Overseas operations 307 

Department of Transportation 308 

Department of Agriculture 309 

Department of Energy 310 


Chapter 6 

Review of recommendations for a national program in weather modifica- Page 

tion 313 

Introduction ^Jy 

Summaries of major weather modification reports 314 

Final report of the Advisory Committee on Weather Control — 314 
Weather and climate modification: Report of the Special Com- 
mission on Weather Modification 315 

Weather and climate modification: Problems and prospects 317 

A recommended national program in weather modification 318 

A national program for accelerating progress in weather modifica- 
tion 320 

Weather and climate modification: Problems and progress 321 

Annual reports to the President and Congress by NACOA 323 

Need for a national weather modification research program 324 

The Federal role in weather modification 325 

Trends and analysis 326 

Chapter 7 

State and local activities in weather modification 331 

Overview of State weather modification activities 331 

Introduction 331 

North American Interstate Weather Modification Council 333 

Survey and summary of State interests and activities in weather 

modification 340 

State contacts for information on weather modification activities. 343 

Non-Federal U.S. weather modification activities 343 

Analysis of calendar year 1975 projects 344 

Preliminary analysis of projects for calendar years 1976-77_ 347 
General discussion of local and regional weather modification policy 

activities „ 348 

Weather modification activities within particular States 351 

California 352 

State weather modification law and regulations 352 

Weather modification projects 353 

State-sponsored emergency projects 356 

Illinois 358 

Illinois weather modification law and its administration 358 

Operational projects 359 

Research activities 360 

Kansas 361 

Kansas Weather Modification Act 361 

Research activities 362 

Operational activities 364 

Emergenc}- Drought Act of 1977 364 

North Dakota 365 

Weather modification law and administration of regulations- 365 

Authority and organization for local projects 370 

North Dakota operational projects in 1975 and 1976 371 

South Dakota 376 

Utah 381 

Washington 382 

Chapter 8 

Private activities in weather modification 385 

Introduction 385 

Commercial weather modifiers 386 

Scope and significance of contract activities 386 

Summary of contract services 386 

Evaluation and research by commercial firms 388 

Participation in Federal research programs 389 

Weather modification organizations 389 

Professional organizations 389 

Weather Modification Association 390 

American Meteorological Society 395 



Opposition to weather modification 399 

General discussion 399 

Opposition to the seeding project above Hungry Horse Dam. 399 

Tri-State Natural Weather Association 400 

Citizens for the Preservation of Natural Resources 402 

Chapter 9 

Foreign'activities in weather modification 405 

Introduction 405 

World Meteorological Organization register of weather modification 

projects 408 

Description of weather modification activities in some foreign nations. 412 

The Union of Soviet Socialist Republics 412 

Overview of projects in the U.S.S.R 412 

Summary of weather modification and related atmospheric 

research in the U.S.S.R 413 

Israel 415 

Australia 416 

Canada 418 

Mexico 419 

People's Republic of China 420 

Kenya 421 

Republic of South Africa 422 

Rhodesia 423 

India 423 

The Swiss hail experiment 424 

Chapter 10 

International aspects of weather modification 427 

Introduction 427 

Convention on the prohibition of military or any other hostile use of 

environmental modification techniques 429 

Development of the treaty 429 

Criticism of the convention 431 

Activities since the United Nations approval of the convention.. 432 
Activities of the World Meteorological Organization in weather 

modification 433 

Precipitation enhancement program (PEP) 434 

Other WMO activities in weather modification 436 

Registration and reporting of weather modification projects. 436 

WMO conferences on weather modification 436 

Typhoon and serious storm modification 437 

Global atmospheric research programme 437 

Legal aspects of weather modification 437 

United Nations Conference on the Human Environment 438 

Declaration of the United Nations Conference on the Human 

Environment 438 

Action Plan for the Human Environment 438 

Earthwatch Program 439 

Study of Man's Impact on Climate 439 

Other international activities 440 

United States/Canadian agreement 440 

North American Interstate Weather Modification Council 440 

Congressional activities 441 

Weather modification as a weapon of war 441 

Senate Resolution 71, prohibiting environmental modification 

as a weapon of war 441 

Congressional activities related to hostile use of weather 

modification, 1974-76 442 

Other Congressional actions relating to weather modification 443 

Senate Concurrent Resolution 67 — U.S. participation in the 

world weather program 443 

National Weather Modification Policy Act of 1976 444 

Senate Resolution 49 444 



U.S. foreign policy 444 

Various executive branch proposals 445 

National Advisory Committee on Oceans and Atmosphere 447 

Activities in 1977 448 

Chapter 11 

Legal aspects of weather modification 449 

Domestic 449 

Private rights in the clouds 449 

Liability for weather modification 453 

Defenses which may be raised against claims of liability 456 

Interstate allocation of atmospheric water 457 

Methods of controlling weather modification 459 

Congressional authority under the Constitution to regulate or 

license weather modification activities 461 

Federalism 461 

The commerce clause 461 

The commerce clause generally 462 

The commerce clause and the regulation of navigable 

waters 463 

Limitations on the commerce power 464 

Fiscal powers 465 

War powers 466 

Property power 466 

Treaty power 467 

Conclusion 467 

International 468 

Certain hostile uses of weather modification are prohibited 471 

Nations are responsible for environmental conduct which causes 

injury or damage in or to other nations 471 

Nations are liable for injuries sustained by aliens within their 
territory caused by tortuous conduct in violation of inter- 
national law 472 

Nations or their citizens may be liable for injury and damage 
they caused to citizens of another nation occurring in that 

nation 472 

Chapter 12 

Economic aspects of weather modification 475 

Introduction 475 

Economic setting 476 

Economic aspects of weather modification procedures 477 

Fog dispersal 477 

Precipitation augmentation 478 

Orographic cloud seeding 478 

Convective cloud seeding 478 

Precipitation augmentation and energy considerations 479 

Hail suppression 480 

Lightning suppression and reduction in storm damage 480 

Analytic methods for economic analysis 481 

Case studies of the economics of weather modification 482 

Hungry Horse Area, Montana 482 

Connecticut River basin 483 

State of Illinois 483 

Nine-county Southeastern Crop Reporting District, South Dakota, 483 

Colorado River 484 

Conclusions 486 

Chapter 13 

Ecological effects of weather modification 487 

Introduction 487 

Modification of weather and climate 487 

Ecology and ecological systems — 487 

Knowledge of ecological implications of applied weather modifi- 
cation technologies 488 



Important variables 490 

Temporal considerations 491 

Season of modification effort 491 

Duration of effort: Short- v. long-term 491 

Regularity of modification effort 491 

Ecosystem type 492 

Aquatic v. terrestrial systems 492 

Cultivated v. natural systems 492 

Arid v. humid systems 492 

Cumulative and synergistic effects 492 

Effects of silver iodide* 493 

Deliberate weather modification 496 

Precipitation enhancement 496 

Increased rainfall 496 

Snowpack augmentation 497 

Severe storm abatement 498 

Fog dispersal 499 

Hail suppression 499 

Alteration or arrest of lightning discharges 499 

Inadvertent weather modification 499 

Extra-area effects 499 

Long-term, climatic, and global implications 500 

Summary and conclusions 501 


A. Statement on weather modification in Congressional Record of 

June 17, 1975, by Congressman Gilbert Gude, containing White 

House statement on Federal weather modification policy 503 

B. Department of Defense statement on position on weather modification. 509 

C. Text of United Nations Convention on the prohibition of military 

or any other hostile use of environmental modification techniques 510 

D. State statutes concerning weather modification 514 

Arizona 515 

California 516 

Colorado 520 

Connecticut 528 

Florida 529 

Hawaii 531 

Idaho 531 

Illinois 533 

Iowa 541 

Kansas 543 

Louisiana 549 

Minnesota 550 

Montana 554 

Nebraska 557 

Nevada 565 

New Hampshire 571 

New Mexico 571 

New York 573 

North Dakota 573 

Oklahoma 584 

Oregon 59 1 

Pennsylvania 599 

South* Dakota 604 

Texas 600 

Utah 612 

Washington 613 

West Virginia 618 

Wisconsin 622 

Wyoming 622 

E. List of State contacts for further information on weather modification 

activities within the States 625 

F. Agreement on exchange of information on weather modification 

between the United States of America and Canada 627 


G. Weather modification activities in the United States during calendar Pa?e 

year 1975 630 

H. Selected bibliography of publications in weather modification 641 

I. Public laws dealing specifically with weather modification 640 

J. Summary of language in congressional documents supporting public 

works appropriations for the Bureau of Reclamation's atmospheric 

water resources program 655 

K. Membership and charter of the U.S. Department of Commerce 

Weather Modification Advisory Board 660 

L. Rules and regulations and required forms for submitting information 
on weather modification activities to the National Oceanic and 
Atmospheric Administration, U.S. Department of Commerce, in 

accordance with requirements of Public Law 92-205 662 

M. Selected State rules and regulations for the administration of State 

weather modification statutes 676 

Illinois 676 

Kansas 6 S3 

North Dakota 691 

Utah 707 

Washington 712 

N. Documents of the Weather Modification Association 717 

O. Policy statement of the American Meteorological Society on purposeful 

and inadvertent modification of weather and climate 722 

P. Reporting agencies of member countries and questionnaire circulated 
to receive weather modification information from members of the 

World Meteorological Organization 724 

Q. Report of the World Meteorological Organization/ United Nations 
Environment programme informal meeting on legal aspects of 

weather modification 727 

R. Text of Senate Resolution 71; considered, amended, and agreed to 

July 11, 1973 734 

S. Reported cases on weather modification 740 

T. Glossary of selected terms in weather modification 741 

34-857—79 2 


Weather modification is generally considered to be the deliberate 
effort to improve atmospheric conditions for beneficial human pur- 
poses — to augment water supplies through enhanced precipitation or 
to reduce economic losses, property damages, and deaths through 
mitigation of adverse effects of hail, lightning, fog, and severe storms. 
Not all weather modification activities, however, have been or can be 
designed to benefit everyone, and some intentional operations have 
been used, or are perceived to have been used, as a weapon of war 
to impede the mobility or tactical readiness of an enemy. Further- 
more, environmental change is also effected unintentionally and with- 
out any purpose at all, as man inadvertently modifies the weather and 
climate, whether for better or worse scientists are not certain, through 
activities such as clearing large tracts of land, building urban areas, 
and combustion of fossil fuels. 

Historically, there have been attempts, often nonscientific or pseudo- 
scientific at best, to change the weather for man's benefit. Until the 
20th century, however, the scientific basis for such activities was 
meager, with most of our current understanding of cloud physics and 
precipitation processes beginning to unfold during the 1930's. The 
modern period in weather modification is about three decades old, dat- 
ing from events in 1946, when Schaefer and Langmuir of the General 
Electric Co. demonstrated that a cloud of supercooled water droplets 
could be transformed into ice crystals when seeded with dry ice. Soon 
afterward it was discovered that fine particles of pure silver iodide, 
with crystal structure similar to that of ice, were effective artificial 
ice nuclei, and that seeding clouds with such particles could produce 
ice crystals at temperatures just below freezing. Silver iodide remains 
the most often used material in modern "cloud seeding." 

By the 1950's, many experimental and operational weather modifi- 
cation projects were underway; however, these early attempts to 
augment precipitation or to alter severe storm effects were often in- 
conclusive or ineffective, owing to improper experimental design, lack 
of evaluation schemes, and the primitive state of the technology. 
Through research programs over the past two decades, including 
laboratory studies and field experiments, understanding of atmos- 
pheric processes essential to improved weather modification tech- 
nology has been advanced. Sophisticated evaluation schemes have been 
developed, using elaborate statistical tools; there has also been im- 
provement in measuring instruments and weather radar systems ; and 
simulation of weather processes using numerical models and high 
speed computers has provided further insights. Meanwhile, commer- 
cial weather modifiers, whose number decreased dramatically along 
with the total area of the United States covered by their operations 
after the initial surge of the 1950 era, have grown in respectability and 
competence, and their operations have incorporated improvements as 
they benefited from their accumulated experience and from the re- 



suits of research projects. Since such operations are designed for prac- 
tical results, such as increased precipitation or reduced hail, however, 
the sophisticated evaluation procedures now used in most research 
projects are most often not used, so that the effectiveness of the opera- 
tions is frequently difficult to assess. 

Weather modification is at best an emerging technology. Progress in 
development of the technology over the past 30 years has been slow, 
although there has been an increased awareness of the complex nature 
of atmospheric processes and a steady improvement in basic under- 
standing of those processes which underlie attempts at deliberate modi- 
fication of weather phenomena. Though most cloud-seeding practices 
are based on a common theory and form the basis for a number of seed- 
ing objectives, there are really a series of weather modification 
technologies, each tailored to altering a particular atmospheric pheno- 
menon and each having reached a different state of development and 
operational usefulness. For example, cold fog clearing is now consid- 
ered to be operational, while, at the other extreme, the abatement of 
severe storms such as hurricanes remains in the initial research phase. 
Development progress for each of these technologies appears to be 
much less a function of research effort expended than a dependence on 
the fundamental atmospheric processes and the ease by which they can 
be altered. There continues to be obvious need for further research and 
development to refine those few techniques for which there has been 
some success and to advance technology where progress has been slow 
or at a virtual standstill. 

The following summary provides a reasonably accurate assessment 
of the current status of weather modification technology : 

1. The only routine operational projects are for clearing cold fog. 
Research on warm fog has yielded some useful knowledge and good 
models, but the resulting technologies are so costly that they are usable 
mainly for military purposes and very busy airports. 

2. Several longrunning efforts to increase winter snowpack by seed- 
ing clouds in the mountains suggest that precipitation can be increased 
by some 15 percent over what would have happened "naturally." 

3. A decade and a half of experience with seeding winter clouds on 
the U.S. west coast and in Israel, and summer clouds in Florida, also 
suggest a 10- to 15-percent increase over "natural" rainfall. Hypotheses 
and techniques from the work in one area are not directly transferable 
to other areas, but will be helpful in designing comparable experiments 
with broadly similar cloud systems. 

4. Numerous efforts to increase rain by seeding summer clouds in the 
central and western parts of the United States have left many questions 
unanswered. A major experiment to try to answer them — for the High 
Plains area — is now in its early stages. 

5. It is scientifically possible to open holes in wintertime cloud layers 
by seeding them. Increasing sunshine and decreasing energy consmp- 
tion may be especially relevant in the northeastern quadrant of the 
United States. 

0. Some $10 million is spent by private and local public sponsors for 
cloud-seeding efforts, but these projects arc not designed as scientific 
experiments and it is difficult to say for sure that operational cloud 
seeding causes the claimed results. 


7. Knowledge about hurricanes is improving with good models of 
their behavior. But the experience in modifying that behavior is primi- 
tive so far. It is inherently difficult to find enough test cases, especially 
since experimentation on typhoons in the Western Pacific has been 
blocked for the time being by international political objections. 

8. Although the Soviets and some U.S. private operators claim some 
success in suppressing hail by seeding clouds, our understanding of the 
physical processes that create hail is still weak. The one major U.S. 
held experiment increased our understanding of severe storms, but 
otherwise proved mostly the dimensions of what we do not yet know. 

9. There have been many efforts to suppress lightning by seeding 
thunderstorms. Our knowledge of the processes involved is fair, but the 
technology is still far from demonstrated, and the U.S. Forest Service 
has recently abandoned further lightning experiments. 1 

Modification processes may also be initiated or triggered inadvert- 
ently rather than purposefully, and the possibility exists that society 
may be changing the climate through its own actions by pushing on 
ceitain leverage points. Inadvertently, man is already causing measur- 
able variations on the local scale. Artificial climatic effects have been 
observed and documented on local and regional scales, particularly in 
and downwind of heavily populated industrial areas where waste heat, 
particulate pollution and altered ground surface characteristics are 
primarily responsible for the perceived climate modification. The cli- 
mate in and near large cities, for example, is warmer, the daily range 
of temperature is less, and annual precipitation is greater than if the 
cities had neA^er been built. Although not verifiable at present, the time 
may not be far off when human activities will result in measurable 
large-scale changes in weather and climate of more than passing sig- 
nificance. It is important to appreciate the fact that the role of man at 
this global level is still controversial, and existing models of the gen- 
eral circulation are not yet capable of testing the effects in a conclusive 

Nevertheless, a growing fraction of current evidence does point to 
the possibility of unprecedented impact on the global climate by hu- 
man activities, albeit the effects may be occurring below the threshold 
where they could be statistically detected relative to the record of nat- 
ural fluctuations and. therefore, could be almost imperceptible amid 
the ubiquitous variability of climate. But while the degree of influence 
on world climate may as yet be too small to detect against the back- 
ground of natural variations and although mathematical models of 
climatic change are still imperfect, significant global effects in the 
future are inferred if the rates of growth of industry and population 

For over 30 years both legislative and executive branches of the 
Federal Government have been involved in a number of aspects of 
weather modification. Since 1947 about 110 weather modification bills 
pertaining to research support, operations, grants, policy studies, regu- 
lations, liabilities, activity reporting, establishment of panels and com- 
mittees, and international concerns have been introduced in the Con- 

1 Weather Modification Advisory Board. "A U.S. Policy to Enhance the Atmospheric 
Environment," Oct. 21, 1977. In testimony by Harlan Cleveland. Weather modification. 
Hearing before the Subcommittee on the Environment and the Atmosphere, Committee on 
Science and Technology. U.S. House of Representatives. 93th Cong., 1st sess., Oct. 26, 
1977, Washington, U.S. Government Printing Office, 1977. pp. 28-30. 


gress. Resolutions, mostly concerned with using weather modification 
ns a weapon and promotion of a United Nations treaty banning such 
activities, have also been introduced in both houses of the Congress ; 
one such resolution was passed by the Senate. 

Six public laws specifically dealing with weather modification have 
been enacted since 1953, and others have included provisions which are 
in some way relevant to weather modification. Federal weather modi- 
fication legislation has dealt primarily with three aspects — research 
program authorization and direction, collection and reporting of in- 
formation on weather modification activities, and the commissioning 
of major policy studies. In addition to direction through authorizing 
legislation, the Congress initiated one major Federal research pro- 
gram through a write-in to an appropriations bill; this program 
regularly receives support through additional appropriations beyond 
recommended OMB funding levels. 

There are two Federal laws currently in effect which are specifically 
concerned with weather modification. Public Law 92-205, of Decem- 
ber 18, 1971, and its amendments requires the reporting of all non- 
Federal activities to the Secretary of Commerce and publication "from 
time to time" of summaries of such activities by the Secretary of 
Commerce. 2 The National Weather Modification Policy Act of 1976 
(Public Law 94-490), enacted October 13, 1976, directed the Secretary 
of Commerce to conduct a major study on weather modification and to 
submit a report containing a recommended Federal policy and Fed- 
eral research program on w T eather modification. The Secretary ap- 
pointed a non-Government Weather Modification Advisory Board to 
conduct the mandated study, the report on which is to be submitted 
to the Secretary for her review and comment and subsequent trans- 
mittal to the President and the Congress during 1978. It is expected 
that, following receipt of the aforementioned report, the Congress will 
consider legislation on Federal weather modification policy, presuma- 
bly during the 96th Congress. 

Congressional interest in weather modification has also been mani- 
fested in a number of hearings on various bills, in oversight hearings 
on pertinent ongoing Federal agency programs, in consideration of 
some 22 resolutions having to do with weather modification, and in 
commissioning studies on the subject by congressional support 

The principal involvement in weather modification of the Federal 
Government has been through the research and development programs 
of the several Federal departments and agencies. Although Federal 
research programs can be traced from at least the period of World 
War II, the programs of most agencies other than the Defense Depart- 
ment were not begun until the 1950's and 1960's. These research and 
development programs have been sponsored at various times by at 
least eight departments and independent agencies — including the De- 
partments of Agriculture, Commerce, Defense, Energy, Interior, and 
Transportation, the National Aeronautics and Space Administration 
(NASA), and the National Science Foundation (NSF). In fiscal year 

2 Although Federal agencies were excluded from the requirements of this not. upon agreement, the agencies also submit information on their weather mollification 
projects to tlie Secretary of Commerce, so that there is a single repository for information 
on nil weather modification activities conducted within the United States. 


1978 six agency programs were reported, those of Transportation and 
NASA having been phased out, while that of Agriculture was severely 

Total funding for Federal weather modification research in fiscal 
year 1978 is estimated at about $17 million, a decline from the highest 
funding level of $20 million reached in fiscal year 1976. The largest 
programs are those of the Departments of Interior and Commerce and 
of the NSF. The NSF has supported weather modification research 
over a broad spectrum for two decades, although its fiscal year 1978 
funding was reduced by more than 50 percent, and it is not clear that 
more than the very basic atmospheric science supportive of weather 
modification will be sponsored hereafter by the Foundation. 

The present structure of Federal organization for weather modifi- 
cation research activities is characterized essentially by the mission- 
oriented approach, whereby each of the agencies conducts its own 
program in accordance with broad agency goals or under specific direc- 
tions from the Congress or the Executive. Programs have been loosely 
coordinated through various independent arrangements and/or advi- 
sory panels and particularly through the Interdepartmental Commit- 
tee for Atmospheric Sciences (ICAS). The ICAS, established in 1959 
by the former Federal Council for Science and Technology, provides 
advice on matters related to atmospheric science in general and has 
also been the principal coordinating mechanism for Federal research 
in weather modification. 

In 1958 the National Science Foundation was designated lead agency 
for Federal weather modification research by Public Law 85-510, a 
role which it maintained until 1968, when Public Law 90-407 removed 
this responsibility from NSF. No further action was taken to name a 
lead agency, although there have been numerous recommendations to 
designate such a lead agency, and several bills introduced in the Con- 
gress would have named either the Department of the Interior or the 
Department of Commerce in that role. During the 10-year period from 
1958 to 1968 the NSF promoted a vigorous research program through 
grants to various research organizations, established an Advisory 
Panel for Weather Modification, and published a series of 10 annual 
reports on weather modification activities in the United States. Since 
1968 there has been a lapse in Federal weather modification policy and 
in the Federal structure for research programs, although, after a 
hiatus of over 3 years, the responsibility for collecting and disseminat- 
ing information on weather modification activities was assigned to the 
Commerce Department in 1971. An important consideration of any 
future weather modification legislation will probably be the organiza- 
tional structure of the Federal research program and that for admin- 
istration of other related functions which may be the responsibility of 
the Federal Government. Options include a continuation of the present 
mission-oriented approach with coordination through the ICAS or a 
similar interagency body, redesignation of a lead agency with some 
autonomy remaining with the several agencies, or creation of a single 
agency with control of all funding and all research responsibilities. 
The latter could be an independent agency or part of a larger depart- 
ment ; it would presumably also administer other aspects of Federal 
weather modification responsibilities, such as reporting of activities, 


regulation and licensing, and monitoring and evaluation of operations, 
if a n}' or all of these functions should become or continue to be services 
performed at the Federal level. 

In addition to specific research programs sponsored bv Federal agen- 
cies, there are other functions related to weather modification which 
are performed in several places in the executive branch. Various Fed- 
eral advisory panels and committees and their staffs — established to 
conduct in-depth studies and prepare comprehensive reports, to pro- 
vide advice and recommendations, or to coordinate Federal weather 
modification programs — have been housed and supported within exec- 
utive departments, agencies, or offices. The program whereby Federal 
and non-Federal U.S. weather modification activities are reported to 
the Government is administered by the National Oceanic and Atmos- 
pheric Administration (NOAA) within the Commerce Department. 
The State Department negotiates agreements with other nations which 
might be affected by U.S. experiments and has arranged for Federal 
agencies and other U.S. investigators to participate in international 
meteorological projects, including those in weather modification. In 
the United Nations, the United States has been active in promoting the 
adoption of a treaty banning weather modification as a military 

In accordance with the mandates of several public laws or self-ini- 
tiated bv the agencies or interagency committees, the executive branch 
of the Federal Government has undertaken a number of major weather 
modification policy studies over the past 25 years. Each of the com- 
pleted major studies was followed by a report which included findings 
and recommendations. The most recent study is the one noted earlier 
that is being conducted by the Weather Modification Advisory Board 
on behalf of the Secretarv of Commerce, pursuant to requirements of 
the National Weather Modification Policy Act of 1976. Nearly all 
previous studies emphasized the needs for designation of a lead agency, 
increased basic meteorological research, increased funding, improve- 
ment of support and cooperation from agencies, and consideration of 
legal, socioeconomic, environmental, and international aspects. Other 
recommendations have included improvement of program evaluation, 
studv of inadvertent effects, increased regulation of activities, and a 
number of specific research projects. Although some of the recom- 
mended activities have been undertaken, many have not resulted in 
specific actions to date. Almost invariably it was pointed out in the 
studies that considerable progress would result from increased fund- 
ing. Although funding for weather modification research has increased 
over t he past 20 years, most funding recommendations have been for 
considerably higher levels than those provided. Since fiscal year 1976, 
the total Federal research funding for weather modification research 
hn=. in fact, decreased. 

Most States in the Nation have some official interest in weather 
modification ; 29 of them have some form of law which relates to such 
activities, usually concerned with various facets of regulation or con- 
trol of operations within the Slate and sometimes pertaining to au- 
thorization for funding research and/or operations at the State or 
local level. A State's weather modification law usually reflects its gen- 
eral policy toward weather modification; some State laws tend to en- 


courage development and use of the technology, while others dis- 
courage such activities. 

The current legal regime regulating weather modification has been 
developed by the States rather than the Federal Government, except 
in the areas of research support, commissioning studies, and requiring 
reporting of activities. The various regulatory and management func- 
tions which the States perform include: (1) issuance, renewal, sus- 
pension, and revocation of licenses and permits; (2) monitoring and 
collecting of information on activities through requirements to main- 
tain records, submission of periodic activity reports, and inspection 
of premises and equipment; (3) funding and managing of State or 
locally organized operational and/or research programs ; (4) evalua- 
tion and advisory services to locally organized public and private op- 
erational programs within the State; and (5) miscellaneous admin- 
istrative activities, including the organization and operation of State 
agencies and boards which are charged with carrying out statutory 
responsibilities. Administration of the regulatory and managerial re- 
sponsibilities pertaining to weather modification within the States is 
accomplished through an assortment of institutional structures, in- 
cluding departments of water or natural resources, commissions, and 
special governing or advisory groups. Often there is a combination of 
two or more of these agencies or groups in a State, separating func- 
tions of pure administration from those of appeals, permitting, or ad- 
visory services. 

Involvement in weather modification operational and research pro- 
grams varies from State to State. Some support research only, while 
others fund and operate both research and operational programs. In 
some cases funding only is provided to localities, usually at the county 
level, where operational programs have been established. The recent 
1976-77 drought led some Western States to initiate emergency cloud- 
seeding programs as one means of augmenting diminishing water sup- 
plies. Research conducted by atmospheric and other scientists at State 
universities or other research agencies may be supported in part with 
State funds but is often funded by one of the major Federal weather 
modification programs, such as that of the Bureau of Reclamation or 
the National Science Foundation. In a few cases. States contribute 
funds to a Federal research project which is conducted jointly with 
the States and partly within their borders. 

In 1975, 1976, and 1977, respectively, there were 58, 61, and 88 non- 
federally supported weather modification projects, nearly all opera- 
tional, conducted throughout the United States. These projects were 
sponsored by community associations, airlines, utilities, private in- 
terests, municipal districts, cities, and States. Eighty-five percent of 
all projects in the United States during 1975 were carried out west of 
Kansas City, with the largest number in California. In that State 
there were 11 proipets in each of the vears 1975 and 1976, and 20 
projects during 1977. The majority of these operational projects were 
designed to increase precipitation; others were intended for sup- 
pression of hail or dispersal of fogs, the latter principally at airports. 

In most instances, the principal beneficiaries of weather modification 
are the local or regional users, who include farmers and ranchers, 
weather-related industries, municipalities, airports, and utilities — 


those individuals and groups whose economic well-being and whose 
lives and property are directly subject to adverse consequences of 
drought or other severe weather. It is at the local level where the need 
to engage in weather modification is most keenly perceived and also 
where possible negative effects from such activities are most apparent 
to some sectors of the population. It follows that both the greatest sup- 
port and the strongest opposition to weather modification projects are 
focussed at the local level. The popularity of a particular project and 
the degree of controversy surrounding it are frequently determined by 
the extent to which local citizens and local organizations have had a 
voice in the control or funding of the project. At the local level, deci- 
sions to implement or to withdraw from a project can most often be 
made with minimum social stress. Indeed, studies have shown that most 
people are of the opinion that local residents or local government offi- 
cials should make decisions on whether or not to use weather modifica- 
tion technology in a given situation. 

Many of the operational weather modification services provided for 
private groups and governmental bodies within the States are carried 
out under contract by commercial firms who have developed expertise 
in a broad range of capabilities or who specialize in particular services 
essential to both operational or research projects. Contracts may cover 
only one season of the year, but a number of them are renewed an- 
nually, with target areas ranging from a few hundred to a few thou- 
sand square miles. In 197G, 6 of the 10 major companies having 
substantial numbers of contracts received about $2.7 million for op- 
erations in the United States, and a few of these companies also had 
contracts overseas. Owing to increased demand for emergency pro- 
grams during the recent drought, it is estimated that 1977 contracts 
totaled about $3.5 million. 

The initial role of the private weather modification operators was to 
sustain activities during the early years, when there was often heated 
scientific controversy with other meteorologists over the efficacy of 
cloud seeding. Later, their operations provided a valuable data base 
which permitted the early evaluation of seeding efforts and estimates 
of potential prospects for the technology, meanwhile growing in com- 
petence and public respect. Today, more often than not, they work 
hand in hand with researchers and, in fact, they often participate in 
research projects, contributing much of their knowhow acquired 
through their unique experiences. 

Important among private institutions concerned with weather modi- 
fication are the professional organizations of which research and op- 
erational weather modifiers and other interested meteorologists are 
members. These include the American Meteorological Society, the 
Weather Modifical ion Association, and the Irrigation and Drainage 
Division of the American Society of Civil Engineers. Through the 
meetings and publications of these organizations the scientific, tech- 
nical, and legal problems and findings on weather modification are 
aired and discussed. These groups also address other matters such as 
statements of weather modification policy, opinions on pending legis- 
lation, social implieations. and professional standards and certifica- 
tion. Tn addition, the North American Interstate Weather Modifica- 
tion Council is an organizai ion whose membership consists of govern- 


ments of U.S. States and Canadian Provinces and the Government of 
Mexico, which serves as a forum for interstate coordination and ex- 
change of information on weather modification. 

Weather modification is often controversial, and both formal and 
informal opposition groups have been organized in various sections 
of the country. Reasons for such opposition are varied and are based 
on both real and perceived adverse consequences from weather modifi- 
cation. Sometimes with little or no rational basis there are charges 
by these groups that otherwise unexplained and usually unpleasant 
weather- related events are linked to cloud seeding. There are also cases 
where some farmers are economically disadvantaged through receiving 
more, or less than optimum rainfall for their particular crops, when 
artificial inducement of such conditions may have indeed been planned 
to benefit those growing different crops with different moisture re- 
quirements. Opposition groups are often formed to protect the legiti- 
mate rights of farmers under such circumstances. 

While the United States is the apparent leader in weather modifi- 
cation research and operations, other countries have also been active. 
Information on foreign weather modification activities is not uni- 
formly documented and is not always available. In an attempt to 
assemble uniform weather modification activities information of its 
member nations, the World Meteorological Organization (WMO) in 
1975 instigated a system of reporting and of maintaining a register on 
such activities. Under this arrangement 25 nations reported weather 
modification projects during 1976, and 16 countries provided similar 
information in 1975. The largest weather modification effort outside 
the United States is in the Soviet Union, where there are both a con- 
tinuing research program and an expanding operational program. The 
latter is primarily a program designed to reduce crop damage from 
hail, the largest such effort in the world, covering about 5 million 
hectares (15 million acres) in 1976. Other countries with weather modi- 
fication programs of some note include Canada, Israel, Mexico, and 
the People's Republic of China. Projects in Rhodesia and the Republic 
of South Africa are not reported through the WMO register since 
these countries are not WMO member nations. 

Recent years have seen increased international awareness of the 
potential benefits and possible risks of weather modification technology 
and increased international efforts to control such activities. The major 
efforts of the international community in this area are to encourage 
and maintain the high level of cooperation which currently exists in 
weather prediction and research and to insure that man's new abilities 
will be used for peaceful purposes. There has been exchange of ideas 
on weather modification through international conferences and 
through more informal exchanges of scientists and research documents. 
As with many scientific disciplines, however, the problems arising 
from use of and experiments with weather modification are not just 
scientific in nature, but are political problems as well. 

In addition to the problems of potential damage to countries through 
commercial or experimental weather modification activities, another 
growing area of concern is that weather modification will be used for 
hostile purposes and that the future will bring weather warfare be- 
tween nations. The United States has already been involved in one 


such instance during the Vietnam war when attempts were made to 
impede traffic by increasing rainfall during the monsoon season. In the 
future, even the perception that weather modification techniques are 
available or in use could lead to an increase in international tensions. 
Natural drought in a region, or any other natural disaster will be 
suspect or blamed on an enemy. 

In light of these problems the international community has made 
scattered attempts both to further the study of weather and its modifi- 
cation and to insure the peaceful use of this new technology. One such 
attempt was the development of the Convention on the Prohibition 
of Military or Any Other Hostile Use of Environmental Modification 
Techniques, which was adopted by the General Assembly of the United 
Nations and opened for signature on May 18. 19TT, at which time it was 
signed by the United States and 33 other nations (though it has not 
yet been submitted to the U.S. Senate for ratification) . Another exam- 
ple of promotion of peaceful use of weather modification is the Pre- 
cipitation Enhancement Program, sponsored by the WMQ, whose aim 
is to plan, set up, and carry out an international, scientifically con- 
trolled precipitation experiment in a semiarid region of the world 
under conditions where the chances are optimal for increasing pre- 
cipitation in sufficient amounts to produce economic benefits. 

The United Nations Conference on the Human Environment, held 
in June 1972 in Stockholm, has been the pivotal point in much recent 
international environmental activity. It too has been an important 
catalyst in international activities relating to weather modification 
through portions of its "Declaration," its "Action Plan for the Human 
Environment," its "Earthwatch Program," and its "Study of Man's 
Impact on Climate." 

Legal issues in weather modification are complex and unsettled. 
They can be considered in at least four broad categories : private rights 
in the clouds, liability for weather modification, interstate legal issues, 
and international legal issues. Since the body of law on weather modi- 
fication is slight, existing case law offers few guidelines to determine 
these issues. Regarding the issue of private rights in the clouds, there 
is no general statutory determination of ownership of atmospheric 
water, so it is often necessary to use analogies to some general common 
law doctrines pertaining to water distribution, although each such 
doctrine has its own disadvantages when applied to weather modifica- 
tion. Some State laws reserve ownership or right to use atmospheric 
water to the State. 

Issues of liability for damage may arise when drought, flooding, 
or other severe weal her phenomena occur following attempts to modify 
the weather. Such issues include causation, nuisance, strict liability, 
trespass, negligence, and charges of pollution of the air and water 
through introduction of artificial nucleants. Statutes of 10 States dis- 
cuss weather modification liability: however, there is much variation 
among the specific provisions of the laws in those States. Before a 
case can be made for liability based on causation, it must be pro\en 
that the adverse weather conditions were indeed induced by the wen: r 
modifier; but, in fact, no one lias ever been able to establish causation 
of damages through such activities in view of the scientific uncer- 
tainties of weather modification. 


Significant issues may arise when weather modification activities 
conducted in one State affect another State as well. There may be, for 
example, the claim that seeding in one State has removed from the 
clouds water that should have fallen in an adjacent State or that 
excessive flooding resulted from cloud seeding in a State upwind. 
Operation of cloud-seeding equipment near the border of one State 
may also violate local or State regulations or prohibitions of such 
operations in that State. There have been some attempts to resolve these 
and other issues through specific legislation in some States and through 
informal bilateral agreements. While no formal compacts currently 
exist, some compacts allocating waters in interstate streams may be 

Because atmospheric processes operate independent of national 
borders, weather modification is inherently of international concern, 
and. international legal issues have similarities to domestic interstate 
activities and dangers. Whereas domestic weather modification law is 
confused and unsettled, international law in this area is barely in the 
formative stage. In time, ramifications of weather modification may 
lead to major international controversy. 

Whereas the potential for long-term economic gains through weather 
modification cannot be denied, current economic analyses are tenuous in 
view of present uncertainty of the technology and the complex nature 
of attendant legal and economic problems. Economic evaluation of 
weather modification activities has therefore been limited to special, 
localized cases, such as the dispersal of cold fog at airports, where 
benefit-cost ratios greater than 5 to 1 have been realized through sav- 
ings in delayed or diverted traffic. It has also been estimated, on the 
basis of a 15-percent increase in snowpack through seeding orographic 
clouds, that about 2 million additional acre-feet of water per year 
could be produced in the Colorado River Basin, at a cost of about 
$1.50 per acre-foot. 

Costs of most weather modification operations are generally small 
in relation to other costs in agriculture, for example, and are normally 
l>elieved to be only a fraction of the benefits which could be achieved 
from successful operations. However, if all the benefits and all the costs 
are considered, benefit-cost ratios may be diminished. While direct co«ts 
and benefits from weather modification are reasonably apparent, in- 
direct costs and benefits are elusive and require further study of 
sociological, legal, and ecological implications. 

There are numerous cases of both real and perceived economic losses 
which one or more sectors of the public may suffer while another 
group is seeking economic advantage through some form of weather 
modification. Overall benefits from weather modification are accord- 
ingly reduced when net gains are determined from such instances of 
mixed economic advantages and disadvantages. In fact, when mecha- 
nisms are established for compensating those who have suffered losses 
resultinof from weather modification, benefits to those groups seeking 
economic gain through such projects will probably be accordingly 

Economically significant weather modification activities will have 
an eventual ecological effect, though appearance of that effect may be 
hidden or delayed by system resilience and/or confused by system 


complexity. Prediction of ecological effects may never be possible with 
any precision; however, the greater the precision with which the 
weather modifier can predict results of his activities, the more pre- 
cisely can the ecologist predict ecological effects. Such effects will 
rarely be sudden or catastrophic, but will result from moderate 
weather-related shifts in rates of reproduction, growth, and mortality 
of plants and animals. Adjustments of plant and animal communities 
will thus occur more slowly in regions of highly variable weather than 
in those with more uniform conditions which are slowly changing with 
some regularity over time. Deliberate weather modification, such as 
precipitation augmentation, is likely to have a greater ecological im- 
pact in semi-arid regions than in humid ones. 

Widespread cloud seeding, using silver iodide, could result in esti- 
mated local, temporary increases in silver concentrations in precipita- 
tion approaching those in natural waters, but exchange rates would be 
an order of magnitude lower than the natural exchange rates. Ex- 
change rates will likely be many orders of magnitude less than those 
rates at which plants and soils are adversely affected. 


1. Weather modification is an emerging technology ; there is a wide 
spectrum of capabilities to modify various weather phenomena, rang- 
ing from the operational readiness of cold fog dispersal to little prog- 
ress beyond initial research in the case of modifying severe storms 
such as hurricanes. 

2. Along with cold fog dispersal, the only other weather modifica- 
tion capability showing near readiness for application is the aug- 
mentation of winter snowpack through seeding mountain cloud sys- 
tems. A probable increase of about 15 percent is indicated by a number 
of experiments and longrunning operational seeding projects in the 
western United States. 

3. Most scientists and weather modification operators agree that 
there is continued need for a wide range of research and development 
activity both to refine weather modification techniques where there 
has been some success and to advance capabilities in modifying other 
weather phenomena where there has been much less or little progress. 

4. Current Federal policy for weather modification research and 
development follows the mission-oriented approach, where each agency 
charged with responsibility for dealing with a particular national 
problem is given latitude to seek the best approach or solution to the 
problem; this approach or solution may involve weather modification. 

5. The structure of Federal organization for weather modification 
reflects the mission-oriented approach which is characteristic of the 
current Federal policy, the programs loosely coordinated through ad- 
visory groups and the Interdepartmental Committee for Atmospheric 

0. The interest of the Congress in weather modification has been 
shown by the introduction of 110 bills related to the subject since 
1017 — of which have become public law — and the consideration of 22 
resolutions on weather modification, one of which was passed by the 

7. A number of major weather modification policy studies have been 
directed by public law or initiated within the executive branch over 


the past 25 years ; most of these studies recommended designation of 
a lead agency, increased basic meteorological research, increased fund- 
ing, improvement of support and cooperation from agencies, and con- 
sideration of legal, socioeconomic, environmental, and international 
aspects. Although some recommended actions have been undertaken, 
others have not seen specific action to date. 

8. While major policy studies have recommended increased funding 
for Federal weather modification, research and development and fund- 
ing has generally increased over the past 20 years, recommended levels 
have been consistently higher than those provided, and funding has 
actually decreased since fiscal year 1976. 

9. With enactment of the National Weather Modification Policy 
Act of 1976 and completion of the major policy study mandated by 
that act, there is a fresh opportunity for the Congress to assess the 
potential usefulness and problems in application of weather modifica- 
tion technology and to establish a new Federal policy for weather 
modification research and operations. 

10. The principal role in regulating weather modification and in 
supporting operational programs has been taken by the States, while 
the role of the Federal Government has been support of research and 
development programs. 

11. The majority of the States (29) have some form of law which 
relates to weather modification, and the general policy of a State 
toward weather modification is usually reflected in the weather modi- 
fication law of that State ; laws of some States tend to encourage devel- 
opment and use of the technology, while others discourage such 

12. The majority of operational weather modification projects in the 
United States (58 of a total of 72, or 80 percent in calendar year 1975) 
are conducted west of Kansas City, and the largest number of projects 
has been in California (20 during 1977) ; most operational projects 
are intended to increase precipitation, while others are designed to 
suppress hail or disperse fog. 

13. Both the greatest support and the strongest opposition to weather 
modification projects are focused at the local level, where the economic 
and personal interests of local organizations and individuals are most 
directly affected; it follows that there is also the least social stress 
when decisions to apply or withhold weather modification are made 
at the local level. 

14. Commercial weather modification operators have substained ac- 
tivities since the early days, after which some operations fell into 
disrepute, providing a valuable data base for evaluation of long-term 
projects and developing expertise over a broad range of capabilities: 
most have incorporated improvements into their technology as they 
have benefited from accumulated experience and from research results. 

15. While the United States is the apparent leader in overall research 
and operational weather modification activities, there have been ap- 
proximately 20 foreign countries in which activities are conducted an- 
nually (25 countries reported such projects for 1976 through the 
register of the World Meteorological Organization) ; the largest for- 
eign program is that of the Soviet Union, whose operational hail 
suppression program covered about 15 million acres in 1976, the largest 
such effort in the world. 


16. The international community has attempted to further the study 
o f weather modification and insure its peaceful use through the recent 
development of a Convention on the Prohibition of Military or Any 
Other Hostile Use of Environmental Techniques (adopted by the 
U.N. General Assembly and opened for signature in May 1977) and 
through sponsorship by the World Meteorological Organization of 
an international precipitation enhancement program. 

17. Legal issues in weather modification are complex and unsettled; 
they include resolution of problems of ownership of atmospheric water, 
issues of liability, conflicting statutes and regulations of respective 

e laws, and the need to develop a regime of relevant international 


18. Although the long-term potential for economic gains through 
weather modification cannot be denied, attempts to quantify benefits 
mnd costs from such activities will in most cases be difficult to undertake 
on a practical basis until the technology is more highly developed and 
control systems are perfected to permit reliable predictions of 

19. Economically significant w r eather modification will always have 
an eventual ecological effect, though appearance of the effect may be 
delayed or hidden by system resilience and/or confounded by system 
complexity ; the more precisely the weather modifier can specify effects 
lie will produce, the more precise can be the ecologist's prediction of 
likely ecological effects. 

20. Modification processes may also be initiated or triggered inad- 
vertently rather than purposefully ; man is already causing measurable 
variations unintentionally on the local scale, and artificial climate 
effects have been observed on local and regional scales. Although not 
veri fiable at present, the time may not be remote when human activities 
will result in measurable large-scale changes in weather and climate 
of more than passing significance. 



(I?y Robert E. Morrison, Specialist in Earth Sciences, Science Policy Research 
Division, Congressional Research Service) 


u It is entirely possible, were he wise enough, that man could produce 
favorable effects, perhaps of enonnous practical significance, trans- 
forming his environment to render it more salutary for his purposes. 
This is certainly a matter which should be studied assiduously and 
explored vigorously. The first steps are clear. In order to control 
meteorological matters at all we nee d to understand them better than 
we now do. When we understand fully ice can at least predict weather 
with assurance for reasonable intervals in the future. 

''With modem analytical devices, with a team of sound background 
and high skills, it is possible today to do a piece of work in this field 
which will render immediate benefits, and carry us for toward a more 
thorough understanding of ultimate possibilities. By all means let us 
get at it." 

— Vanne var Bush 1 


Two decades after completion of a major study and report on 
weather modification by the Advisory Committee on Weather Control 
and after the assertions quoted above, many would agree that some 
of the more fundamental questions about understanding and using 
weather modification remain unsolved. There is a great difference of 
opinion, however, on the state of technology in this field. According 
to Grant, "Some believe that weather modification is now ready for 
widespread application. In strong contrast, others hold that applica- 
tion of the technology may never be possible or practical on any 
substantial scale." 2 It has been demonstrated that at least some atmos- 
pheric phenomena can be modified with some degree of predictable 
success, as a consequence of seeding supercooled clouds with artificial 
ice nuclei, and there is some promise that the present technology will 
be expanded to include a greater scope of weather modification capa- 
bilities. Nevertheless, a systematic approach and reasonable progress 
in development of weather modification technology have been impeded 
by a number of problems. 

Changnon asserts that a continuing and overriding problem restrict- 
ing progress has been the attempt to apply an ill-defined technology 
to increase rain or suppress hail without an adequate scientific under- 

1 From statement of Dec. 2, 1957, quoted in final report of the Advisory Committee on 
Weather Control, Washington, D.C., U.S. Government Printing Office. 1958. vol. I. p. 1. 

2 Grant, Lewis O., "Scientific and Other Uncertainties of Weather Modification. In 
William A. Thomas (editor), Legal and Scientific Uncertainties of Weather Modification. 
Proceedings of a symposium convened at Duke University. Mar. 11-3 2. 1976, by the 
National Conference of Lawyers and Scientists, Durham, N.C., Duke University Press, 
1977, p. 7. 


34-857—79 3 


standing and predictable outcome. 3 Experimentation has been poorly 
conducted, intermittent, or too short ; and "results have not been inte- 
grated with those of other projects so as to develop a continuing thread 
of improving knowledge." 4 

In response to the query as to why progress in weather modification 
lias been so slow, Fleagle identifies three broad, general impediments. 
"First, the physical processes associated with clouds have turned out to 
be especially complex and difficult * * *. A second possibility may be 
that the atmosphere is inherently stable, so that within broad limits, no 
matter what we do to increase precipitation, the results are likely to be 
small and roughly the same * * *. A third reason * * * is that progress 
has been hamstrung by fragmentation of resources, by submarginal 
funding, ineffective planning and coordination, and a general lack of 
administrative toughness and fiscal stability." 5 

Droessler points out the need to "formulate a comprehensive national 
weather modification policy which has the broad support of the scien- 
tific community, the general public, private industry, and the Govern- 
ment," contending that "the greatest deterrent in getting on with the 
task of preparing a satisfactory national policy is the lack of a con- 
sensus about the national goals for weather modification." 6 

Although operational readiness varies from one form of weather 
modification to another, as a result of the degree of understanding and 
the complexity of decisionmaking in given situations, the prospects for 
successful weather modification are sufficiently promising that at- 
tempts to develop effective applications will continue. This was one of 
the major areas of co?isensus at a recent symposium on the uncertainties 
of weather modification : 

There will be increased attempts to modify weather, both because people tend 
to do what is technically possible and because the anticipated benefits of precipi- 
tation augmentation, hail or lightning suppression, hurricane diversion, and other 
activities often exceed the associated costs. 7 

With the inevitable increases in weather modification capabilities 
and the increasing application of these capabilities, the development of 
a technology that is socially useful must be insured through a careful 
analysis of attendant benefits and disbenefits. According to Fleagle. 
et al.. deliberate efforts to modify the weather have thus far had only 
marginal societal impacts; however, as future activities expand, "they 
will probably be accompanied by secondary effects which in many 
instances cannot be anticipated in detail * * *." Consequently, "rational 
policy decisions are urgently needed to insure that activities are di- 
rected toward socially useful goals." 8 

The lack of a capability to deal with impending societal problems 

8 Changnori, Stanley A.. Jr.. "The Federal Role In Weather Modification." bgckgrbund 
paper prepared for use by the U.S. Department of Commerce Weather Modification Advi- 
sory Board. Mar. !). 3 077, p. 5. 

' Ibid., pp. ">-G. 

s Fleagle. Robert O.. "An Analysis of Federal Policies in Weather Modification.'' back- 
ground paper prepared for use by the U.S. Department of Commerce Weather Modification 
Adv:s< rv Hoard. Mar. 1<»77. pp. 17-18. 

« Droessler, Farl (».. "Weather Modification" (Federal Policies. Funding From AIT 
Sources Interagency Coordination), background paper prepared for use of the U.S. Depart- 
ment of Commerce Weather Modification Advisory Board, Mar. l. l!>77. p. 10 

7 Thomas. William A. (editor). "Legal and Scientific Uncertainties of Weather Modifie-i- 
tion," proceedings of a Symposium convened at Duke University. Mar 11-12. 1970, by the 
Vf»'onal Conference of Lawyers and Scientists. Durham, N.C., Dnke Universitv Pres., 
1077, p. vl. 

Flt*agie. Robert r > • -lames A. Crutchfteld, Ralph W. Johnson, and Mohamed F. AbdO, 
"Weather Modification in the PUbllC Interest." Seattle, American Meteorological Society 

and the University of Washington Press, i<>73. p. 3, 31-32. 


and emerging management issues in weather modification has been 
aphoristically summed up in the following statement by Crutchfield: 

Weather modification is in the throes of a serious schizoid process The slow 
and sober business of piecing together the scientific knowledge of weather proc- 
esses developing the capacity to model the complex systems involved, and assess- 
ing systematically the results of modification efforts has led to responsible opti- 
mism about the future of these new technologies. On the other hand, the social 
technology" of evaluation, choice, and execution has lagged badly. Ihe present de- 
cisionmaking apparatus appears woefully inadequate to the extraordinarily ^diffi- 
cult task of fitting weather modification into man s pattern of life m optimal 
fashion There are' too many game plans, too many coaches, and a disconcerting 
proclivity for running hard before deciding which goal line to aim for— or, indeed, 
which field to play on. ,J . . . _ . 

Mounting evidence indicates that weather modification of several types is, 
or may soon become technically feasible. That some groups will derive economic 
or other social benefits from such technology is a spur to action. But a whole 
thunderhead of critical questions looms on the horizon waiting to be resolved 
before any valid decisions can be made about the scale, composition, location, 
and management of possible operations. 9 


In a study for the Interdepartmental Committee for Atmospheric 
Sciences, Homer E. Newell highlighted the potential benefits of inten- 
tional weather modification : 

The Earth's weather has a profound influence on agriculture, forestry, water 
resources, industry, commerce, transportation, construction, field operations, 
commercial fishing, and many other human activities. Adverse effects of weather 
on man's activities and the Earth's resources are extremely costly, amounting 
to billions of dollars per year, sometimes causing irreparable damage as when 
human lives are lost in severe storms. There is, therefore, great motivation 
to develop effective countermeasures against the destructive effects of weather, 
and, conversely, to enhance the beneficial aspects. The financial and other ben- 
efits to human welfare of being able to modify weather to augment water 
supplies, reduce lightning, suppress hail, mitigate tornadoes, and inhibit the full 
development of hurricanes would be very great. 10 

More recently. Louis J. Battan gave the following two reasons, with 
graphic examples, for wanting to change the weather : 

First, violent weather kills a great many people and does enormous property 
damage. A single hurricane that struck East Pakistan in Novemlier 1970 killed 
more than 250,000 people in a single day. Hurricane Camille hit the United States 
in 1969 and did approximately $1.5 billion worth of damage. An outbreak of 
tornadoes in the Chicago area on Palm Sunday of 1965 killed about 250 people, 
and the tornadoes of April 1974 did likewise. Storms kill people and damage 
property, and it is reasonable to ask whether it is necessary for us to accept 
this type of geophysical destruction. I say, "No, it is not — it should be possible 
to do something." 

Second, weather modification involves, and in some respects might control, 
the production of those elements we need to survive. Water and food are cur- 
rently in short supply in many areas, and these shortages almost certainly will 
be more severe in the future. We can develop new strains of wheat and rye and 
corn and soybeans and rice, but all is for naught if the weather fails to coop- 
erate. If the monsoons do not deliver on schedule in India, residents of that 
country starve in large numbers. And if the drought that people have been 
predicting for the last several years does spread over the Great Plains, there 
will be starvation around the world on a scale never before experienced. 

Weather is the one uncontrollable factor in the whole business of agriculture. 
Hail, strong winds, and floods are the scourges of agriculture, and we should 
not have to continue to remain helpless in the face of them. It may be impossible 

9 Crntehfielri. James A.. "Social CVoice and Weather Modification : Concepts and Measure- 
ment of Impact." In W. R. Derrick Sewell (editor). Modifying the Weather: a Social 
Assessment, Victoria, British Columbia. University of Victoria. 1978. p. 1S7. 

10 Newell. Homer E., "A Recommended National Program in Weather Modification." Fed- 
eral Council for Science and Technology, Interdepartmental Committee for Atmospheric 
Sciences, ICAS report No. 10a, Washington, D.C., November 1966, p. 1. 


for us to develop the kind of technology we would like to have for modification 
of weather, but to assume failure in such an important endeavor is a course 
not to be followed by wise men. 11 

Specific statistics on annual losses of life and economic losses from 
property damages resulting from weather-related disasters in the 
United States are shown in table 1, which w r as developed in a recent 
study by the Domestic Council. 12 In the table, for comparison, are 
the fiscal year 1975 expenditures by the Federal Government in 
weather modification research, according to the several categories of 
weather phenomena to be modified. Although it is clear that weather 
disasters can be mitigated only partially through weather modifica- 
tion, even if the technology were fully developed, the potential value, 
economic and otherwise, should be obvious. The following quotation 
from a Federal report written over a decade ago summarizes the full 
potential of benefits to mankind which might be realized through use 
of this technology : 

With advances in his civilization, man has learned how to increase the fruit 
of the natural environment to insure a livelihood. * * * it is fortunate that 
growing knowledge of the natural world has given him an increasing awareness 
of the changes that are occurring in his environment and a' so hopefully some 
means for deliberate modification of these trends. An appraisal of the prospects 
for deliberate weather and climate modification can be directed toward the 
ultimate goal of bringing use of the environment into closer harmony with its 
capacities and with the purposes of man — whether this be for food production, 
relief from floods, assuring the continuance of biologic species, stopping pollu- 
tion, or for purely esthetic reasons. 13 


Property Modification 
damage 1 research 

Weather hazard Loss of life 1 (billions) (millions) 

Hurricanes 2 30 2 $rj. 8 3 $o. 8 

Tornadoes . 2140 2.4 4 1.0 

Hail 5.8 3.9 

Lightning « 110 .1 .4 

Fog M.000 7.5 1.3 

Floods 6 240 8 2.3 

Frost (agriculture) 7 1. 1 

Drought 7 .7 93.4 

Total 1,520 6.7 10.8 

1 Sources: "Assessment of Research on Natural Hazards," Gilbert F. White and J. Eugene Haas, the MIT Press, Cam- 
bridge, Mass., 1975, pp 68, 286, 305, 374; "The Federal Plan for Meteorological Services and Supporting Research, Fiscal 
Year 1976," U.S. Department of Commerce, National Oceanic and Atmospheiic Administration (NOAA), Washington, D.C., 
April 1975, p 9; "Weatheiwise," February 1971, 1972, 1973, 1974, 1975, American Meteorological Society, Boston, Mass.; 
"Summary Report on Weather Modification, Fiscal Years 1969, 1970, 1971," U.S. Department of Commerce, NOAA, Wash- 
ington, D.C., May 1973, pp 72, 81; "Estimating Crop Losses Due to Hail — Wot king Data for County Estimates," U.S. De- 
partment of Agriculture, Economic Research Service, September 1974; "Natural Disasters: Some Empirical and Economic 
Considerations," G. Thomas Sav, National Bureau of Standards, Washington, D.C., February 1974, p 19; Traffic Safety 
magazine, National Safety Council, February 1974. 

2 1970-74 average. 

3 These funds do not include capital investment in research aircraft and instrumentation primarily for hurricane modi- 
fication, which in fiscal year 1975 amounted to $9,200,000. 

4 These funds support theoretical research on modification of extratropical cloud systems and their attendant severe 
storms such as thunderstorms and tornadoes. 

5 1973. 

« 1950-72 average. 

7 Average. 

1 1965-69 average. 

9 These funds support precipitation augmentation research, much of which may not have direct application to drought 

11 Battan, Louis J.. "The Scientific Uncertainties: a Scientisl Responds." in William A. 
Thomas (editor), "Legal and Scientific Uncertainties of Weather Modification." proceed- 
ings of a symposium Convened at Duke University, .Mar. 11-12, 197©, by C e National Con- 
ference of Lawyers and Scientists. Durham. N.C., Duke University Press. 1!)77. p. 20. 

12 U.S Domestic Council. Environmental Resources Committee, Subcommittee on Climate 
Change. "The Federal Rofe in Weather Modification," December i ( ->~r», p. 2. 

u» Special Commission on Weather Modification. "Weather and Climate Modification," 
National Science Foundation. NSF 6G-3, Washington, D.C., Dec. 20, 1965, p. 7. 



The modern period in weather modification is about three decades 
old, dating from events in 1946, when Schaefer and Langmuir demon- 
strated that a cloud of supercooled water droplets could be transformed 
into ice crystals when seeded with dry ice. Activities and interests 
among scientists, the commercial cloud seeders, and Government spon- 
sors and policymakers have exhibited a nearly 10-year cyclic behavior 
over the ensuing years. Each of the three decades since the late 1940's 
has seen an initial burst of enthusiasm and activity in weather modi- 
fication experiments and/or operations; a midcourse period of con- 
troversy, reservations, and retrenchment; and a final period of 
capability assessment and policy examination, with the issuance of 
major Federal reports with comprehensive recommendations on a 
future course. 

The first such period ended with the publication of the final report 
of the Advisory Committee on Weather Control in 1957. 14 In 1959, 
Dr. Robert Brode, then Associate Director of the National Science 
Foundation, summarized the significance of that study in a 1959 
congressional hearing : 

For 4 years the Advisory Committee studied and evaluated public and private 
cloud-seeding experiments and encouraged programs aimed at developing both 
physical and statistical evaluation methods. The final report of the com- 
mittee * * * for the first time placed before the American public a body of 
available facts and a variety of views on the status of the science of cloud 
physics and the techniques and practices of cloud seeding and weather modifica- 
tion. 15 

The year 1966 was replete with Government weather modification 
studies, major ones conducted by the National Academy of Sciences, 
the Special Commission on Weather Modification of the National 
Science Foundation, the Interdepartmental Committee for Atmos- 
pheric Sciences, and the Legislative Reference Service of the Library 
of Congress. During that year, or thereabouts, planning reports were 
also produced by most of the Federal agencies with major weather 
modification programs. The significance of that year of reevaluatiori 
and the timeliness for congressional policy action were expressed by 
Hartman in his report to the Congress : 

It is especially important that a comprehensive review of weather modification 
be undertaken by the Congress at this time, for a combination of circumstances 
prevails that may not be duplicated for many years. For the first time since 
1957 there now exists, in two reports prepared concurrently by the National 
Academy of Sciences and a Special Commission on Weather Modification, created 
by the National Science Foundation, a definitive appraisal of the entire scope 
of this subject, the broad sweep of unsolved problems that are included, and 
critical areas of public policy that require attention. There are currently before 
the Congress several bills which address, for the first time since enactment of 
Public Law 85-510. the question of the formal assignment of Federal authority 
to undertake weather modification programs. And there is increasing demand 
throughout the country for the benefits that weather modification may bring. 16 

14 F^tablishment of the Advisory Committee on Weather Control by the Congress and its 
actJ^ties are discussed in following chapters on the history of weather modification and 
on Federal activities, chs. 2 and 5, respectively. Recommendations of the final report are 
summarized in ch. 6. Other renorts mentioned in the following paragraphs in this section 
are also discussed and referenced in chs. 5 and 6. ■ \ - .. 

15 U.S. Congress. House of Representatives. Committee on Science and Astronautics. 
"Weather Modification." Hearing. Sfith Cong.. 1st sess., Feb. 16, 1959. Washington, JJ.L., 
U.S. Government Printing OfhYp 19^9. p 3. . t _ _ 

16 Hartman, Lawton M. "Weather Modification and Control.' Library of Comrress, 
Legislative Reference Service. Apr. 27. 1966. Issued as a committee print by the Senate 
Committee on Commerce. 89th Cone.. 2d sess., Senate Rept. No. 1139, Washington, 

U.S. Government Printing Office, 1966, p. 1. 


Toward the close of the third decade, a number of policy studies and 
reports appeared, starting in 1973 with a second major study by the 
National Academy of Sciences, and including others by the U.S. Gen- 
eral Accounting Office and by the U.S. Domestic Council. The major 
study of this period was commissioned by the Congress when it enacted 
Public Law 94-490, the National Weather Modification Policy Act of 
1976, in October of 1976. By that law the Secretary of Commerce was 
directed to conduct a study and to recommend the Federal policy and a 
Federal research program in weather modification. That study was 
conducted on behalf of the Secretary of Commerce by a Weather Modi- 
fication Advisory Board, appointed by the Secretary, and the required 
report will be transmitted to the Congress during 1978. The importance 
of that act and its mandated study was assessed by Dr. Robert M. 
White, former Administrator of the National Oceanic and Atmos- 
pheric Administration (NOAA), the Commerce Department agency 
with administrative responsibilities and research programs in weather 
modification : 

The National Weather Modification Policy Act of 197C> * * * will influence 
X( )AA to some degree during the next year, and its effect may have a large impact 
on the agency and the Nation in future years. The comprehensive study of and 
report on weather modification that will result from our implementation of this 
act will provide guidance and recommendations to the President and the Congress 
in the areas of policy, research, and utilization of this technology. We look to this 
study and report as an opportunity to help set the future course of a controversial 
science and technology with enormous potential for henefit to the Nation. 17 

Thus, conditions once more are ripe and the stage has been set, as in 
1957 and again in 1966, for the Congress to act in establishing a defini- 
tive Federal weather modification policy, one appropriate at least for 
the next decade and perhaps even longer. Among other considerations, 
such a policy would define the total role of the Federal Government, 
including its management structure, its responsibilities for research 
and development and for support operations, its authorities for regu- 
lation and licensing, its obligation to develop international cooperation 
in research and peaceful applications, and its function in the general 
promotion of purposeful weather modification as an economically vi- 
able and socially accepted technology. On the other hand, other factors, 
such as constraints arising from public concern over spending, may 
inhibit the development of such policy. 

While some would argue that there exists no Federal policy, at least 
one White House official, in response to a letter to the President, made 
a statement of weather modification policy in 1975: 

A considerable amount of careful thought and study has been devoted to the 
subject of weather modification and what the Federal role and. in particular, the 
role of various agencies should he in (his area. As a result of this study, we have 
developed a general strategy for addressing weather modification efforts which 
we believe provides for an appropriate level of coordination. 

We believe that the agency which is charged with the responsibility for dealing 
with a particular national problem should Ite given the latitude to seek the best 
approach or solution to the problem. In some instances this may involve a form 
of weather modification, while in other instances other approaches may be more 

While we would certainly agree that some level of coordination of weather 
modification research efforts is logical, we do not believe that a program under 

w CJ.S. Congress, Souse of Representatives, Committee on Science and Technology. Sub* 

committi d the EBaTlronmeal snd the Atmosphere. "Briefing «"i the National Oceanic and 

Atmospheric Administration." Hearings. 9.1th Cong., 1st sess., May 17. 18, 1977. Washing- 
Jon. I'.S. Government Printing Ollice, 1977. i». 4-i5. 


the direction of any one single agency's leadership is either necessary or desirable. 
We have found from our study that the types of scientific research conducted by 
agencies are substantially different in approach, techniques, and type of equip- 
ment employed, depending on the particular weather phenomena being addressed. 
Each type of weather modification requires a different form of program manage- 
ment and there are few common threads which run along all programs. 13 

Presumably, there will be a resurgence of congressional interest in 
weather modification policy during the first session of the 96th Con- 
gress, when the aforementioned report from the Secretary of 
Commerce has been reviewed and considered. In view of the recom- 
mendations in numerous recent studies and the opinions of the Weather 
Modification Advisory Board (the group of experts preparing the re- 
port for the Secretary of Commerce) , it seems unlikely that any action 
by the Congress would perpetuate the policy expounded in the White 
House letter quoted above. 

It is expected that this present report, intended as an overall review 
of the subject of weather modification, will be valuable and timely dur- 
ing the anticipated congressional deliberations. 


In the broadest sense, weather modification refers to changes in 
weather phenomena brought on purposefully or accidentally through 
human activity. Weather effects stimulated unintentionally — such as 
urban influences on rainfall or fogs produced by industrial com- 
plexes — constitute what is usually termed inadvertent weather modifi- 
cation. On the other hand, alterations to the weather which are 
induced consciously or intentionally are called planned or advertent 
weather modification. Such activities are intended to influence single 
weather events and to occur over relatively short time spans, ranging 
from a few hours in the case of clearing airport fog or seeding a 
thunderstorm to perhaps a few days when attempts are made to re- 
duce the severity of hurricane winds. Weather modification experi- 
ments or operations can be initiated or stopped rather promptly, and 
changes resulting from such activities are transient and generally 
reversible within a matter of hours. 

Climate modification, by contrast, encompasses changes of long-time 
climatic variables, usually affecting larger areas and with some degree 
of permanence, at least in the short term. Climatic changes are also 
brought about by human intervention, and they might result from 
either unintentional or planned activities. There are numerous ex- 
amples of possible inadvertent climate modification; however, at- 
tempts to alter climate purposefully are only speculative. The con- 
cepts of inadvertent weather and climate modification are defined 
more extensively and discussed fully in chapter 4 of this report. 

The primary emphasis of this report is on intentional or planned 
modification of weather events in the short term for the general bene- 
fit of people, usually in a restricted locality and for a specific time. 
Such benefit may accrue through increased agricultural productiv- 

18 Ross, Norman E., Jr., letter of June 5, 1975. to Congressman Gilbert Gude. This letter 
was the official White House response to a letter of April 25. 1975. from Congressmen 
Giule and Donald M. Fraser and Senator Claiborne Pell, addressed to the President, urging 
that a coordinated Federal program be initiated in the peaceful uses of weather modifica- 
tion. The letter to the President, the replv from Mr. Ross, and comments by Congressman 
Gude appeared in the Congressional Record for June 17. 1975, pp. 19201-19203. (This 
statement from the Congressional Record appears in app. A.) 


ity or other advantages accompanying augmentation of precipitation 
or they may result from mitigation of effects of severe weather with 
attendant decreases in losses of life or property. There are broader 
implications as well, such as the general improvement of weather for 
the betterment of man's physical environment for aesthetic and cul- 
tural reasons as well as economic ones. The following recent definition 
sums up succinctly all of these purposes : 

Weather modification is the deliherate and mindful effort by men and women 
to enhance the atmospheric environment, to aim the weather at human purposes. 1 " 

The specific kinds of planned weather modification usually consid- 
ered, and those which are discussed, in turn, in some detail in chapter 
3, are the following: 

Precipitation enhancement. 

Hail suppression. 

Fog dissipation. 

Lightning suppression. 

Mitigation of effects of severe storms. 
Planned weather modification is usually considered in the context 
of its net benefits to society at large. Nevertheless, it should be recog- 
nized that, in particular instances, benefits to some segment of the 
population may be accompanied by unintended injuries and costs, 
which may be real or perceived, to other segments. There is yet an- 
other aspect of advertent weather modification, which has engendered 
much controversy, both in the United States and internationally, not 
designed for the benefit of those directly affected — the use of weather 
modification for hostile purposes such as a weapon of war. This aspect 
is not a major consideration in this report, although there is some 
discussion in chapters 5 and 10 of congressional concern about such use 
of the technology, and in chapter 10 there is also a review of recent 
efforts by the United Nations to develop a treaty barring hostile use 
of weather modification. 20 

Following this introductory chapter, witli its summary of issues, 
the second chapter sets the historical perspective for weather modi- 
fication, concentrating primarily on activities in the United States to 
about the year 1970, The third chapter attempts to review the scien- 
tific background, the status of technology, and selected technical prob- 
lems areas in planned weather modification; while chapter 4 contains 
a discussion of weather and climate changes induced inadvertently by 
man's activities or by natural phenomena. 

The weather modification activities of the Federal Government — 
those of the Congress and the administrative and program activities 
of the executive branch agencies — are encompassed in chapter 5 ; and 
the findings and recommendations of major policy studies, conducted 
by or on behalf of the Federal Government, are summarized in chap- 
ter 6. The seventh, eighth, and ninth chapters are concerned with 
weather modification activities at the level of State and local govern- 
ments, by private organizations, and in foreign countries, respectively. 

111 :'<m- Modification Advisory Hoard, "A TVS Policy to Enhance the Atmospheric 
Environment," Oct. 21, 1!>77. A discussion paper, included with testimony of Harlan Cleve- 
land, Chairman of the Advisory Hoard, in a congressional hearing: U.S. Congress. House 
of Representatives. Committee on Science and Technology. Subcommittee on the Environ- 
ment and the Atmosphere. Weather Modification. !).".th Cong., 1st sess., Oct. 2(5, 1J>77, 
Washington, D.C., U.S. Government Printing Office, H»77. p. 25. 

211 Copies of the current official position of the I'.S. Department of Defense on weather 
modification and of the draft T T .\ convention prohibiting hostile use of environmental 
modification, respectively, are found in apps. B and C. 


The increasingly important international problems related to weath- 
er modification are addressed in chapter 10, while both domestic and 
international legal aspects are discussed in chapter 11. Chapters 12 
and 13, respectively, contain discussions on economic and ecological 
aspects of this emerging technology. 

The 20 appendixes to the report provide materials that are both sup- 
plementary to textual discussions in the 13 chapters and intended 
to be valuable sources of reference data. In particular, attention is 
called to appendix D, which contains excerpts dealing with weather 
modification from the statutes of the 29 States in which such activities 
are in some way addressed by State law, and to appendix E, which 
provides the names and affiliations of individuals within the 50 States 
who are cognizant of weather modification activities and interests with- 
in the respective States. The reader is referred to the table of contents 
for the subjects of the remaining appendixes. 

Summary or Issues in Planned Weather Modification 

"The issues we now face in weather modification have roots in the 
science and technology of the subject, but no less importantly in the 
politics of Government agencies and congressional committees and in 
public attitudes which grow out of a variety of historical, economic, 
and sociological factors." 21 In this section there will be an identifica- 
tion of critical issues which have limited development of weather 
modification and which influence the ability to direct weather modifi- 
cation in a socially responsible manner. The categories of issues do 
not necessarily correspond with the subjects of succeeding chapters 
dealing with various aspects of weather modification ; rather, they are 
organized to focus on those specific areas of the subject where there 
has been and there are likely to be problems and controversies which 
impede the development and application of this technology. 

The following sections examine technological, governmental, legal, 
economic, social, international, and ecological issues. Since the primary 
concern of this report is with the intentional, planned use of weather 
modification for beneficial purposes, the issues summarized are those 
involved with the development and use of this advertent technology. 
Issues and recommendations for further research in the area of inad- 
vertent weather modification are included in chapter 4, in which that 
general subject is fully discussed. 


In a recent discussion paper, the Weather Modification Advisory 
Board summarized the state of weather modification by concluding 
that "no one knows how to modify the weather very well, or on a very 
large scale, or in many atmospheric conditions at all. The first require- 
ment of a national policv is to learn more about the atmosphere it- 
self." 22 Representative of the state of weather modification science 

21 Fleagle. Crutchfield, Johnson, and Abdo, "Weather Modification in the Public Inter- 
est," 1973, p. 15. . . . . 

22 Weather Modification Advisory Board. "A U.S. Policy To Enhance the Atmospheric 
Environment." Oct. 21, 1977. This discussion paper was included with the testimony ot 
Mr. Harlan Cleveland, Chairman of the Advisory Board, in a recent congressional hearing : 
U.S. Congress, House of Representatives, Committee on Science and Technology, Subcom- 
mittee on the Environment and the Atmosphere. "Weather Modification. 9oth Cong., 1st 
sess. Oct. 26, 1977, Washington, D.C., U.S. Govt. Print. Off., 1977, p. 25. 


and technology is the following commentary on the state of under- 
standing in the case of precipitation enhancement, or rainmaking as it 
is popularly called : 

Today, despite the fact that modern techniques aimed at artificial stimulation 
of rain rest upon sound physical principles, progress is still fairly slow. The 
application of these principles is complicated by the overwhelming complexity 
of atmosheric phenomena. It is the same dilemna that meteorologists face when 
they attempt to predict weather. In both cases, predicting the evolution of 
atmospheric processes is limited by insufficient knowledge of the effects produced 
by the fairly well-known interactive mechanisms governing atmospheric phenom- 
ena. Moreover, the temporal and spatial variability of atmospheric phenomena 
presents an additional difficulty. Since any effects that are produced by artificial 
intervention are always imposed upon already active natural processes, assess- 
ment of the consequences becomes even more difficult. 23 

Grant recognizes the current progress and the magnitude of remain- 
ing problems when he says that : 

Important^and steady advances have been made in developing technology 
for applied weather modification, but complexity of the problems and lack of 
adequate research resources and commitment retard progress. Advances have 
been made in training the needed specialists, in describing the natural and 
treated cloud systems, and in developing methodology and tools for the necessary 
research. Nevertheless, further efforts are required. 24 

Though it can be argued that progress in the development of weather 
modification has been retarded by lack of commitment, ineffective 
planning, and inadequate funding, there are specific scientific and tech- 
nical problems and issues needing resolution which can be identified 
beyond these management problems and the basic scientific problem 
quoted above with respect to working with the atmosphere. Particular 
technical problems and issues at various levels which continue to affect 
both research and operational activities are listed below : 

1. There is substantial diversity of opinion, even among informed 
scientists, on the present state of technology for specific types of 
weather modification and their readiness for application and with 
regard to weather modification in general.- 5 

% 2. There are many who view weather modification only as a drought- 
relief measure, expecting water deficits to be quickly replenished 
through its emergency use; however, during such periods weather 
modification is limited by less frequent opportunities ; it should, in- 
stead, be developed and promoted for its year-round use along with 
other water management tools.- 

3. The design and analysis of weather modification experiments is 
intimately related to the meteorological prediction problem, which 
needs further research, since the evaluation of any attempt to modify 
the atmosphere depends on a comparison between some weather pa- 
rameter and an estimate of what would have happened naturally. 

4. Many of the problems which restrict Understanding and predic- 
tion of weather modification phenomena stem from imprecise knowl- 
edge of fundamental cloud processes; the level of research in funda- 

2:1 Dennis, Arnett S., and A. Ge^in. "Recommendations for Future Research in Weatlier 
Modification," U.S. Department <»i" Commerce, National Oceanic and Atmospheric Admin- 
istration, Environmental Research Laboratories. Boulder, Colo.. November 1077. p. VI. 

-"Grant. "Scientific and Other Uncertainties of Weather .Modification," 1977. p. 17. 

88 Sec table 2, ch. D. ">!>. 

-• Silverman. Bernard A., "What Do We Need In Weather Modification?" In preprints 
of the Sixth Conference on Planned and Inadvertent Weather .Modification, Oct. lO-l.'i, 
1077, Champaign, 111., Boston, American Meteorological Society, 1977, p. 308. 


mental cloud physics and cloud modeling has not kept pace with 
weather modification activity. 27 

5. Progress in the area of weather modification evaluation meth- 
odology has been slow, owing to the complexity of verification prob- 
lems and to inadequate understanding of cloud physics and dynamics. 

6. Most operational weather modification projects, usually for the 
sake of economy or in the anticipation of achieving results faster and 
in greater abundance, fail to include a satisfactory means for project 

7. There are difficulties inherent in the design and evaluation of any 
experiment or operation which is established to test the efficacy of 
any weather modification technique, and such design requires the 
inclusion of proper statistical methods. 

8. In view of the highly varying background of natural weather 
phenomena, statistical evaluation of seeding requires a sufficiently 
long experimental period: many research projects just barely fail 
to achieve significance and credibility because of early termination; 
thus, there is a need for longer commitment for such projects, perhaps 
5 to 10 years, to insure that meaningful results can be obtained. 2S 

9. There is a need to develop an ability to predict possible adverse 
weather effects which might accompany modification of specific 
weather phenomena : for example, the extent to which hail suppression 
or diminishing hurricane winds might also reduce beneficial precipi- 
tation, or the possibility of increasing hailfall or incidence of light- 
ning from efforts to stimulate rainfall from cumulus clouds. 29 

10. The translation of cloud-seeding technologies demonstrated in 
one area to another geographical area has been less than satisfactory; 
this has been especially so in the case of convective cloud systems, 
whose differences are complex and subtle and whose classification is 
complicated and sometimes inconsistent. 

11. There is increasing evidence that attempts to modify clouds 
in a prescribed target area have also induced changes outside the 
target area, resulting in the so-called downwind or extended area 
effect : reasons for this phenomenon and means for reducing negative 
results need investigation. 

1*2. There is the possibility that cloud seeding in a given area and 
during a given time period has led to residual or extended time effects 
on weather phenomena in the target area beyond those planned from 
the initial seeding. 

13. The conduct of independent cloud-seeding operations in adjacent 
locations or in the neighborhood of weather modification experiments 
may cause contamination of the atmosphere so that experimental 
results or estimates of operational success are biased. 

14. There have been and continue to be conflicting claims as to 
the reliability with which one can conduct cloud-seeding operations 
so that the seeding agent is transported properly from the dispensing 
device to the clouds or portions of the clouds one seeks to modify. 

27 Hosier. C. L.. "Overt Weather Modification.*' Reviews of Geophysics and Space Phys- 
ics, vol. 12. Xo. 3, August 1974, p. 526. 

28 Simpson. Joanne, "What Weather Modification Needs." In preprints of the Sixth 
Conference on Planned and Inadvertent Weather Modification. Oct. 10-13, 1977. Cham- 
paign. 111.. Boston. American Meteorological Society. 1977, p. 306. 

29 Hosier, "Overt Weather Modification,' - 1974, p. 325. 


15. There is need to develop, improve, and evaluate new and cur- 
rently used cloud-seeding materials and to improve systems for deliv- 
ery of these materials into the clouds. 

16. There is need to improve the capability to measure concentra- 
tions of background freezing nuclei and their increase through seed- 
ing; there is poor agreement between measurements made with various 
ice nucleus counters, and there is uncertainty that cloud chamber 
measurements are applicable to real clouds. 30 

IT. In order to estimate amounts of fallen precipitation in weather 
modification events, a combination of weather radar and raingage 
network are often used; results from such measurement systems have 
often been unsatisfactory owing to the quality of the radar and its 
calibration, and to uncertainties of the radar-raingage intercalibration. 

18. There is continuing need for research in establishing seedability 
criteria ; that is, definition of physical cloud conditions when seeding 
will be effective in increasing precipitation or in bringing about some 
other desired weather change. 

10. Mathematical models used to describe cloud processes or account 
for interaction of cloud systems and larger scale weather systems 
greatly oversimplify the real atmosphere; therefore, model research 
must be coupled with field research. 31 


The basic problem which encompasses all governmental weather 
modification issues revolves about the question of the respective roles, 
if any, of the Federal, State, and local governments. Resolution of this 
fundamental question puts into perspective the specific issues of where 
m the several governmental levels, and to what extent, should goals be 
set, policy established, research and/or operations supported, activities 
regulated, and disputes settled. Part of this basic question includes 
the role of the international community, considered in another section 
on. international issues; 32 the transnational character of weather modi- 
fication may one day dictate the principal role to international orga- 

Role of the Federal Government 

Because weather modification cannot be restricted by State bound- 
aries and because the Federal Government has responsibilities for re- 
source development and for reduction of losses from natural hazards, 
few would argue that the Federal Government ought not to have some 
interest and some purpose in development and possible use of weather 
modification technolo<rv. The following broad and specific issues on 
the role of the Federal Government in weather modification are among 
those which may be considered in developing a Federal policy: 

1. Should a maior policy analysis be conducted in an attempt to re- 
late weather modification to the Xatioivs broad goals; that is, improv- 
ing human health and the qualit v of life, maintaining national security, 
providing sufficient energy supplies, enhancing environmental quality, 
and the production of food and fiber? Barbara Farhar suggests that 
such a study has not been, but ought to be. undertaken. 33 

™ Fbld. 

m Fleagle et al., "Weather Modification in tUo Public interest." 197^. n St. 

n = Sop n. 2& 

"Farhar, Barbara C. "The Societal Imidieations of Weather Modification: a TCeview 
of issues Toward m National Policy.*' Background paper prepared f«r the U.S. Department 
of Commerce Weather ModinVatlonAdvisory Hoard, Mar. 1, 1977, p. 2. 


2. Should the Federal Government commit itself to planned weather 
modification as one of several priority national goals ? It can be argued 
that such commitment is important since Federal program support and 
political attitudes have an important overall influence on the develop - 
ment and the eventual acceptance and application of this technology. 

3. Is there a need to reexamine, define, and facilitate a well-balanced, 
coordinated, and adequately funded Federal research and development 
program in weather modification ? Many argue that the current Fed- 
eral research program is fragmented and that the level of funding is 

4. Is there a suitable Federal role in weather modification activities 
beyond that of research and development — such as project evaluation 
and demonstration and operational programs? If such programs are 
advisable, how can they be identified, justified, and established ? 

5. Should the practice of providing Federal grants or operational 
services by Federal agencies to States for weather modification in times 
of emergency be reexamined, and should procedures for providing such 
grants and services be formalized ? It has been suggested that such as- 
sistance in the past has been haphazard and has been provided after it 
was too late to be of any practical benefit. 

6. Should the organizational structure of the Federal Government 
for weather modification be reexamined and reorganized ? If so, what 
is the optimum agency structure for conducting the Federal research 
program and other functions deemed to be appropriate for the Federal 

7. TThat is the role of the Federal Government, if any, in regulation 
of weather modification activities, including licensing, permitting, 
notification, inspection, and reporting? If such a role is to be modified 
or expanded, how should existing Federal laws and/or regulations be 
modified ? 

8. If all or any of the regulatory functions are deemed to be more ap- 
propriate for the States than for the Federal Government, should the 
Federal Government consider mandating minimum standards and 
some uniformity among State laws and regulations? 

9. Should the Federal Government attempt to develop a means ade- 
quate for governing the issues of atmospheric water rights between 
States, on Federal lands, and between the United States and neighbor- 
ing countries ? 

10. Where federally sponsored research or possible operational 
weather modification projects occupy the same locale as local or 
State projects, with the possibility of interproject contamination, 
should a policy on project priorities be examined and established? 

11. Should the Federal Government develop a policy with regard 
to the military use of weather modification and the active pursuit of 
international agreements for the peaceful uses of weather modifica- 
tion? This has been identified as perhaps one of the most important 
areas of Federal concern. 34 

12. Is there a need to examine and define the Federal responsibility 
for disseminating information about the current state of weather 
modication technology and about Federal policy, including the capa- 
bility for providing technical assistance to the States and to others? 

fS *Farhar Barbara C. "What r>o°s Weatber Modification Need"- In preprints of the 
Sixth Conference on Planned and Inadvertent Weather Modification, Oct. 10-13, 1977, 
Champaign. 111., Boston, American Meteorological Society, 1977, p. 299. 


13. Should there be a continuing review of weather modification 
technology capabilities so that Federal policy can be informed regard- 
ing the readiness of technologies for export to foreign nations, with 
provision of technical assistance where and when it seems feasible? 35 

14. How does the principle of cooperative federalism apply to 
weather modification research projects and possible operations carried 
out within the States ? Should planning of projects with field activities 
in particular States be done in consultation with the States, and should 
cooperation with the States through joint funding and research efforts 
be encouraged ? 

15. What should be the role of the single Federal agency whose 
activities are most likely to be affected significantly by weather modi- 
fication technology and whose organization is best able to provide 
advisory services to the States— the U.S. Department of Agriculture? 
Among the several agencies involved in weather modification, the 
Department of Agriculture has demonstrated least official interest 
and lias not provided appreciable support to development of the 
technology. 36 

Roles of State and local go vernments 

State and local 37 governments are in man}' ways closer to the 
public than the Federal Government — often as a result of more direct 
contact and personal acquaintance with officials and through greater 
actual or perceived control by the voters. Consequently, a number of 
weather modification functions, for both reasons of practical effi- 
ciency and social acceptance, may be better reserved for State and/or 
local implementation. Since weather phenomena and weather modifica- 
tion operations cannot be restricted by State boundaries or by bound- 
aries within States, however, many functions cannot be carried out 
in isolation. Moreover, because of the economy in conducting research 
nnd development on a common basis — and perhaps performing other 
functions as well — through a single governmental entity, such as an 
agency or agencies of the Federal Government, it may be neither 
feasible nor wise for State governments (even less for local jurisdic- 
tions) to carry out all activities. 

Thus, there are activities which might best be reserved for the States 
(and possibly for local jurisdictions within States), and those which 
more properly belong to the Federal Government. In the previous 
l ist of issues on the role of the Federal Government, there was allusion 
to a number of functions which might, wholly or in part, be the re- 
sponsibility of either Federal or State governments; most of these 
will not be repeated here. Issues and problems concerned primarily 
with State and local government functions are listed below: 

1. State weather modification laws. Where they exist, are nonuni- 
form in their requirements and specifications for licensing, permitting, 
inspection, reporting, liabilities, and penalties for violations. More- 
over, some State laws and policies favor weather modification, while 
ot hers oppose 1 he technology. 

2. Authorities for funding operational and research projects with- 
in States and local jurisdictions within States, through public funds 


: " Changnon, "The Federal Role in Weather Modification." |p. 11. 

37 ,f Local" bere refers broadly to any jurisdiction below the State level : it could laelucto 
cities, townships, counties, groups of counties, water districts, or any other organized area 
Operating under public authority. 


or through special tax assessments, vary widely and, except in a few 
States, do not exist. 

3. Decisionmaking procedures for public officials appear to be often 
lacking; these could be established and clarified, especially as the pos- 
sibility of more widespread application of weather modification tech- 
nology approaches. 

4. Many public officials, usually not trained in scientific and en- 
gineering skills, often do not understand weather modification tech- 
nology, its benefits, and its potential negative consequences. Some 
training of such officials could contribute to their making wise de- 
cisions on the use of the technology, even without complete informa- 
tion on which to base such decisions. 

5. Many weather modification decisions have had strong political 
overtones, with some legislators and other public officials expressing 
their views or casting their votes allegedly on the basis of political 
expediency rather than on the basis of present or potential societal 

6. State and local authorities may need to provide for the education 
of the general public on the rudiments of weather modification, on its 
economic benefits and disbenefits. and on other societal aspects. 

7. To keep communication channels open, mechanisms such as pub- 
lic hearings could be established to receive comments, criticisms, and 
general public sentiments on weather modification projects from in- 
dividual citizens and from various interest groups. 

8. Criteria and mechanisms have not been established for compen- 
sating those individuals or groups within States who might be eco- 
nomically injured from weather modification operations. 

9. Questions of water rights within States, as well as between States, 
have not been addressed and/or resolved in a uniform manner. 


Legal issues in weather modification are complex and unsettled. 
They can be discussed in at least four broad categories : 

1. Private rights in the clouds ; 

2. Liability for weather modification ; 

3. Interstate legal issues ; and 

4. International legal issues, 38 

The body of law on weather modification is slight, and existing case 
law offers few guidelines to determine these issues. It is often neces- 
sary, therefore, to analogize weather modification issues to more set- 
tled areas of law such as those pertaining to water distribution. 

Private rights in the clouds 

The following issues regarding private rights in the clouds may be 
asked : 

Are there any private rights in the clouds or in the water which 
may be acquired from them ? 

Does a landowner have any particular rights in atmospheric 
water ? 

Does a weather modifier have rights in atmospheric water \ 

^Questions on regulation or control of weather modification activities through licensing 
and permitting, while of a basic legal nature, are related to important administrative func- 
tions and are dealt with under issues concerned with Federal and State activities. 


Some State statutes reserve the ownership or right to use atmospheric 
water to the State. 39 

There is no general statutory determination of ownership of atmos- 
pheric water and there is no well-developed body of case law. Conse- 
quently, analogies to the following general common law doctrines may 
be helpful, but each has its own disadvantages when applied to weather 
modification : 

1. The doctrine of natural rights, basically a protection of the land- 
owner's right to use his land in its natural condition (i.e., precipita- 
tion is essential to use of the land as are air, sunlight, and the soil 

2. The ad coelum doctrine which states that whoever owns the land 
ought also to own all the space above it to an indefinite extent. 

3. The doctrine of riparian rights, by which the one owning land 
which abuts a watercourse may make reasonable use of the writer, sub- 
ject to similar rights of others whose lands abut the watercourse. 

4. The doctrine of appropriation, which gives priority of right based 
on actual use of the water. 

5. The two main doctrines of ownership in the case of oil and gas 
(considered, like water, to be "fugitive and migratory" substances) ; 
that is, (a) the non-ownership theory, by which no one owns the oil and 
gas until it is produced and anyone may capture them if able to do so; 
and (b) the ownership-in-place theory, by which the landowner has the 
same interest in oil and gas as in solid minerals contained in his land. 

6. The concept of "developed water," that is, water that would not 
be available or would be lost were it not for man's improvements. 

7. The concept of "imported water," that is, water brought from one 
watershed to another. 

Liability for weather modification 

Issues of liability for damage may arise when drought, flooding, or 
other severe weather phenomena occur following attempts to modify 
the weather. Such issues include causation as well as nuisance, strict 
liability, trespass, and negligence. Other issues which could arise relate 
to pollution of the air or water through introduction of artificial nu- 
cleants such as silver iodide, into the environment. While statutes of 
10 States discuss weather modification liability, there is much varia- 
tion among the specific provisions of the laws in those States. 40 

Before any case can be made for weather modification liability 
based upon causation it must be proven that the adverse weather con- 
ditions were indeed brought about by the weather modifier, a very 
heavy burden of proof for the plaintiff. In fact, the scientific uncer- 
tainties of weather modi Heal ion are such that no one has ever been able 
to establish causation of damage through these activities. As weal her 
modification technology is improved, however, the specter of a host of 
liability issues is expected to emerge as evidence for causation becomes 
more plausible. 

While the general defense of the weather modifier against liability 
charges is that causation has not been established, he may also use as 
further defense the arguments based upon immunity, privilege, con- 
sent , and waste. 

• Sec p. 4.">o, ch. 1 1. and app. n. 

M Sec discussion p. 453 in ch. 11 and app. D. 


Interstate legal issues 

When weather modification activities conducted in one State affect 
another State as well, significant issues may arise. The following- 
problem categories are examples of some generally unresolved inter- 
state issues in weather modification : 

1. There may be the claim that cloud seeding in one State has removed 
from the clouds water which should have fallen in a second State or 
that excessive flooding in a neighboring State has resulted from seed- 
ing in a State upwind. 

2. Operation of cloud-seeding equipment near the border in one State 
may violate local or State ordinances which restrict or prohibit weather 
modification in an adjacent State, or such operations may conflict with 
regulations for licensing or permitting of activities within the bor- 
dering State. 

Some States have attempted to resolve these issues through specific 
legislation and through informal bilateral agreements. 41 Another ap- 
proach would be through interstate compact, though such compacts re- 
quire the consent of Congress. No compacts specifically concerned with 
weather modification currently exist, though some existing compacts 
allocating waters in interstate streams may be applicable to weather 

International legal issues 

Because atmospheric processes operate independent of national 
borders, weather modification is inherently of international concern. 
International legal issues have similarities to domestic interstate activi- 
ties and dangers. The following serious international questions, which 
have arisen in conjunction with a developing capability to modify the 
weather, have been identified by Orfield : 42 

Do countries have the right to take unilateral action in all 
weather modification activities? 

What liability might a country incur for its weather modifica- 
tion operations which [might] destroy life and property in a 
foreign State? 

On what theory could and should that State base its claim ? 
The primary international legal issue regarding weather modifica- 
tion is that of liability for transnational injury or damage, which could 
conceivably result from any of the following situations : 

(1) injury or damage in another nation caused by weather 
modification activities executed within the United States; 

(2) injury or damage in another nation caused by weather 
modification activities executed in that nation or a third nation by 
the United States or a citizen of the United States ; 

(3) injury or damage in another nation caused by weather 
modification activities executed in an area not subject to the juris- 
diction of any nation (e.g., over the high seas), by the United 
States or a citizen thereof ; and 

(4) injury or damage to an alien or an alien's property within 
the United States caused by weather modification activities exe- 
cuted within the United States. 

41 See discussion p. 457 in ch. 11 and app. D. 

42 Orfield, Michael B.. "Weather Genesis and Weather Neutralization: a New Approach 
to Weather Modification," California Western International Law Journal, vol. 6, no. 2, 
spring 1976, p. 414. 

34-S57— 79 4 


Whereas domestic weather modification law is confused and unset- 
tled, international law in this area is barely in the formative stage. In 
time, ramifications of weather modification may lead to major interna- 
tionl controversy. 43 


The potential for long-term economic gains through weather modi- 
fication cannot be denied ; however, current, economic analyses are tenu- 
ous in view of present uncertainty of the technology and the complex 
nature of attendant legal and economic problems. Meaningful economic 
evaluation of weather modification activities is thus limited to special, 
localized cases, such as the dispersal of cold fog at airports, where bene- 
fit-cost ratios greater than 5 to 1 have been realized through savings in 
delayed or diverted traffic. Various estimated costs for increased pre- 
cipitation through cloud seeding range from $1.50 to $2.50 per acre- 
foot in the western United States. 

fsy/es complicating economic analyses of weather modification 

Costs of most weather modification operations are usually relatively 
small and are normally believed to be only a fraction of the benefits 
obtained through such operations. However, if all the benefits and all 
the costs are considered, benefit-cost ratios may be diminished. While 
direct costs and benefits from weather modification are reasonably 
obvious, indirect costs and benefits are elusive and require further study 
of sociological, legal, and ecological implications. 

In analyzing benefit-cost ratios, some of the following considerations 
need to be examined : 

Weather modification benefits must be considered in terms of 
the costs for achieving the same objectives as increased precipita- 
tion, e.g., through importation of water, modified use of agricul- 
tural chemicals, or introduction of improved plant strains. 

Costs for weather modification operations are so low in compari- 
son with other agricultural investments that farmers may gamble 
in spending the 5 to 20 cents per acre for operations designed to 
increase rainfall or suppress hail in order to increase yield per 
acre, even though the results of the weather modification opera- 
tions may be doubtful. 

Atmospheric conditions associated with prolonged droughts are 
not conducive to success in increasing precipitation; however, 
under these conditions, it is likely that increased expenditures 
may be made for operations which offer little hope of economic 

Increased precipitation, obtained through a weather modifica- 
tion program sponsored and funded by a group of farmers', can 
also benefit other farmers who have not shared in the costs; thus, 
the benefit-cost ratio to those participating in the program is 
higher than it need be if all share in its costs. 

As weather modification technology develops and programs be- 
come more 1 sophisticated', increased costs for equipment and labor 
will increase direct costs to clients: indirect costs resulting from 
increased State license and permit fees and liability insurance for 
operators will probably also be passed on to the customer. 

I: s»'c ch. 10 on International aspects and i>. 4<;s. ch. 11; on International legal aspects of 
wpa i her modification. 


The sophistication of future programs will likely incur addi- 
tional costs for design, evaluation, and program information ac- 
tivities, along with supporting meteorological prediction services; 
these costs will be paid from public funds or by private clients, in 
either case reducing the overall benefit-cost ratios. 

Ultimate costs for compensation to those incurring disbenefits 
from weather modification operations will offset overall benefits 
and thus reduce bene fit -cost ratios. 

Weather modification and conflicting interests 

There are numerous cases of both real and perceived economic losses 
which one or more sectors of the public may suff er while another group 
is seeking economic advantage through some form of weather modi- 
fication. Overall benefits from weather modification are accordingly 
reduced when net gains are computed from such instances of mixed 
economic advantages and disadvantages. Benefits to the parties seek- 
ing economic gain through weather modification will be directly re- 
duced at such time when mechanisms are established for compensating 
those who have suffered losses. The following are some examples of 
such conflicting situations : 

Successful suppression of hail may be valuable in reducing crop 
damage for orchardists while other agricultural crops may suffer 
f rom decrease of rain concomitant with the hail decrease. 

Additional rainy days may be of considerable value to farmers 
during their growing season but may be detrimental to the finan- 
cial success of outdoor recreational enterprises. 

Increased snowpack from orographic cloud seeding may be 
beneficial to agricultural and hydroelectric power interests but 
increases the costs for maintaining free passage over highways 
and railroads in mountainous areas. 

Successful abatement of winds from severe storms, such as those 
of hurricanes, may result in decreased precipitation necessary for 
agriculture in nearby coastal regions or may redistribute the ad- 
verse storm effects, so that one coastal area is benefitted at the ex- 
pense of others. 


It has been said that "weather modification is a means toward so- 
cially desired ends, not an end in itself. It is one potential tool in a set 
of possible societal adjustments to the vagaries of the weather. Iden- 
tifying when, where, and how to use this tool, once it is scientifically 
established, is the primary need in weather modification." 44 It is likely 
that, in the final analysis, the ultimate decisions on whether weather 
modification should and will be used in any given instance or will be 
adopted more generally as national or State programs depends on 
social acceptance of this tool, no matter how well the tool itself has 
been perfected. That this is increasingly the case has been Suggested by 
numerous examples in recent years. Recently Silverman said : 

Weather modification, whether it he research or operations, will not progress 
wisely, or perhaps at all, unless it is considered in a context that includes everyone 

M Fnrhar. Barbara C. "What Does Weather Modification Need ?" In preprints of the Sixth 
Conference on rianr.pd and Inadvertent Weather Modification. October 10-13, 1977. Cham- 
paign* 111. Boston. American Meteorological Society, 1977. p. 296. 


that may be affected. We must develop and provide a new image of weather 
modification. 45 

Regardless of net economic benefits, a program is hard to justify 
when it produces obvious social losses as well as gains. 

Research in the social science of weather modification has not kept 
pace with the development of the technology, slow as that has been. 
In time, this failure may be a serious constraint on further develop- 
ment and on its ultimate application. In the past, organized opposition 
has been very effective in retarding research experiments and in cur- 
tailing operational cloud-seeding programs. Thus, there is need for an 
expanded effort in understanding public behavior toward weather 
modification and for developing educational programs and effective 
decisionmaking processes to insure intelligent public involvement in 
eventual application of the technology. 

Social issues discussed in this section are those which relate to public 
behavior and public response to weather modification, while societal 
issues are generally considered to include economic, legal, and other 
nontechnical issues as Veil as the social ones. These other aspects of 
societal issues were discussed in preceding sections. In the subsections 
to follow there are summaries of social implications of weather modifi- 
cation, the need for public education, and the problem of 

Social factors 

It has been said that social factors are perhaps the most elusive and 
difficult weather modification externalities to evaluate since such fac- 
tors impinge on the vast and complex area of human values and at- 
titudes. 46 Fleagle, et al., identified the following important social 
implications of weather modification, which would presumably be 
taken into account in formulation of policies : 47 

1. The individuals and groups to be affected, positively or negatively, by tlie 
project must be defined. An operation beneficial to one party may actually barm 
another. Or an aggrieved party may hold the operation responsible * * ::: for 
damage * * * which might occur at the same time or following the modification. 

2. The impact of a contemplated weather modification effort on the genera! 
well-being of society and the environment as a whole must be evaluated. Con- 
sideration should be given to conservationists, outdoor societies, and other 
citizens and groups representing various interests who presently tend to ques- 
tion any policies aimed at changes in the physical environment. It is reasonable 
and prudent to assume that, as weather modification operations expand, question- 
ing and opposition by the public will become more vocal. 

3. Consideration must be given to the general mode of human behavior in 
response to innovation. There are cases where local residents, perceiving a cause 
and effect relationship between economic losses from severe weather and nearby 
weather modification operations, have continued to protest, and even to threaten 
violence, after all operations bave been suspended. 

4. The uniqueness and complexity of certain weather modification operations 
must be acknowledged, and special attention should be given to their social and 
legal implications. The cases of hurricanes and tornadoes are especially perti- 
nent. Alteration of a few degrees in the path of a hurricane may result in its 
missing a certain area * * * and ravaging * * * instead, a different one. The decision 
on whether such an operation is justified can reasonably be made only at the 
highest level, and would need to be based on the substantial scientific finding 
thai the anticipated damages would be loss than those originally predicted h td 
the hurricane been allowed to follow its course. 

1 b Silverman, Bernard A. "What Do We Need in Weather Modification?" In preprints of 
tli<' Sixth Conference on Planned and [nadvertenl Weather Modification, October 10—13, 
litTT. Champaign, ill.. Boston, American Meteorological Society. u»77. p. 310. 

ia Flengle, Crutchfleld, Johnson, and Abdo. "Weather Modification in the Public Interest." 
1074. p. :',7-38. 

*• Ibid., p. 38-40. 


5. Attention must be given to alternatives in considering a given weather 
modification proposal. The public may prefer some other solution to an attempt 
at weather tampering which may be regarded as predictable and risky. Further- 
more, alternative policies may tend to be comfortable extensions of existing 
policies, or improvements on them, thus avoiding the public suspicion of inno- 
vation. In an area such as weather modification, where so many uncertainties 
exist, and where the determination or assigning of liability and responsibility 
are far from having been perfected, public opposition will surely be aroused. 
Any alternative plan or combination of plans will have its own social effects, 
however, and it is the overall impact of an alternative plan and the adverse 
effects of not carrying out such a plan which, in the final analysis, should guide 
decisions on alternative action. 

6. Finally, it is important to recognize that the benefits from a weather modi- 
fication program may depend upon the ability and readiness of individuals 
to change their modes of activity. The history of agricultural extension work 
in the United States suggests that this can be done successfully, but only with 
some time lag, and at a substantial cost. Social research studies suggest that 
public perception of flood, earthquake, and storm hazards is astonishingly casual. 

Need for public education on weather modification 

The previous listing of social implications of weather modification 
was significantly replete with issues derived from basic human atti- 
tudes. To a large extent these attitudes have their origin in lack of in- 
formation, misconceptions, and even concerted efforts to misinform by 
organized groups which are antagonistic to weather modification. As 
capabilities to modify weather expand and applications are more wide- 
spread, it would seem probable that this information gap would also 
widen if there are no explicit attempts to remedy the situation. "At the 
very least," according to Fleagle, et al., "a large-scale continuing pro- 
gram of education (and perhaps some compulsion) will be required if 
the potential social gains from weather modification are to be realized 
in fact," 48 Whether such educational programs are mounted by the 
States or by some agency of the Federal Government is an issue of 
jurisdiction and would likely depend on whether the Federal Govern- 
ment or the States has eventual responsibility for management of op- 
erational weather modification programs. Information might also be 
provided privately by consumer groups, professional organizations, 
the Aveather modification industry, or the media. 

It is likely that educational programs would be most effective if a 
variety of practical approaches are employed, including use of the 
news media, publication of pamphlets at a semitechnical level, semi- 
nars and hearings, and even formal classes. Probably the latter cate- 
gories would be most appropriate for civic groups, Government offi- 
cials, businessmen, or other interests who are likely to be directly 
affected by contemplated operations. 

The following list of situations are examples of public lack of under- 
standing which could, at least in part, be remedied through proper 
educational approaches : 

There is much apprehension over claims of potential d^rger of a 
long-lasting nature on climate, which could supposedly result 
from both inadvertent and planned modification of the weather, 
with little insight to distinguish between the causes and the scales 
of the effects. 

There have been extravagant claims, propagated through ig- 
norance or by deliberate distortion by antagonistic groups, about 

48 Ibid., p. 40. 


the damaging effects of cloud seeding on ecological systems, human 
lien 1th. and air and water quality. 

The controversies between opposing groups of scientists on the 
efficacy of weather modification technologies and between scien- 
tists and commercial operators on the readiness of these technolo- 
gies for application has engendered a mood of skepticism and 
even mistrust of weather modification on the part of a public 
which is largely uninformed on technical matters. 

The public has often been misinformed by popular news media, 
whose reporters seek to exploit the spectacular in popular weather 
modification "stories" and who, themselves usually uninformed in 
technical aspects of the subject, tend to oversimplify and distort 
the facts associated with a rather complex science and technology. 

There has been an organized effort on the part of groups opposed 
to weather modification to mount an educational program which 
runs counter to the objectives of informing the public about the 
potential benefits of a socially acceptable technology of weather 

Portions of the public have acquired a negative impression that 
meteorologists and Government officials concerned with weather 
modification are irresponsible as a result of past use. or perceived 
present and future use. of the technology as a weapon of war. 

Lack of information to the public has sometimes resulted in 
citizen anger when it is discovered that a seeding project has been 
going on in their area for some time without their having been 
informed of it. 


"The nature of wenther processes and the current knowledge about 
them require that most human decisions as to weather modification 
must be made in the face of uncertainty. This imposes special re- 
straints on public agencies and it increases the difficulty of predict- 
ing how individual farmers, manufacturers, and others who are 
directly affected by weather would respond to changes in leather 
Characteristics. 5 ' 49 The situation since 1965 when this statement was 
made has changed little with resrard to predictability of weather 
processes and their modification. There has also been little progress 
toward developing decisionmaking processes which can be applied, 
should the need arise, on whether or not weather modification should 
be emploved. 

A number of studies on social attitudes indicate that the preference 
of most cit izens is that decisionmaking in such areas as use or restraint 
from use of weather modification should be at the local level. owim>- 
to the feeling that citizens' rights and property are best protected 
when decisions are made bv officials over whom they have the most 
direct; control. Farhar savs that evidence suggests that one important 
condition for public acceptance of weather modification technology 
is public involvement in the decision process, especially in civic 
derisions.™ Procedures must then be developed for enabling {peal 

49 Special Commission on Wcnther Modification. "Weather and Climate Modification." 
NRF or, irto.~. p uc. 

» F.-irlisir. Bar nun) P. "The Pnldie Derides Al<ont Weather Modification."' Environment 

and Behavior, vol. 9. No. September 1 077. p. .".07. 


officials, probably not technically trained, to make such decisions 
intelligently. Such decisions must be based both on information 
received from Federal or State teclmical advisers and on the opinions 
of local citizens and interest groups. 


International agreements regarding weather modification experi- 
ments and operations have been very limited. There exists a United 
States-Canada agreement, which requires consultation and notifica- 
tion of the other country when there is the possibility that weather 
modification activities of one country could affect areas across the 
border. 51 Earlier understandings were reached between the United 
States and Canada concerning experiments over the Great Lakes and 
with the IJnited Kingdom in connection with hurricane modification 
research in the Atlantic. 52 Recent attempts to reach agreement with 
the Governments of Japan and the People's Republic of China for 
U.S. experiments in the Far East on modification of typhoons were 
unsuccessful, though such research was encouraged by the Philip- 
pines. There is current intention to reach an agreement with Mexico 
on hurricane research in the eastern Pacific off that nation's coast. 

During 1976, 25 nations reported to the World Meteorological Orga- 
nization that they had conducted weather modification activities. 53 
There have been two principal international activities, dealing with 
somewhat different aspects of weather modification, in recent years. 
One of these is the preparation and design of a cooperative experi- 
ment under the auspices of the World Meteorological Organization, 
called the Precipitation Enhancement Experiment (PEP) ; while the 
other is the development of a convention by the United Nations on 
the prohibition of hostile use of environmental modification. 54 

The following international considerations on research and opera- 
tional weather modification activities can be identified : 

1. There is a common perception of a need to insure that the current 
high level of cooperation which exists in the international community 
with regard to more general meteorological research and weather re- 
porting will be extended to development and peaceful uses of planned 
weather modification. 

2. There is now no body of international law which can be applied to 
the potentially serious international questions of weather modification, 
such as liability or ownership of atmospheric water resources. 55 

3. Past use by the United States, and speculated current or future 
use by various countries, of weather modification as a weapon have 
raised suspicions as to the possible intent in developing advertent 
weather modification technology. 

4. There have been charges that weather modification research activi- 
ties were used to divert severe weather conditions away from the 

r,t The United States-Canada agreement on weather modification is reproduced in nop. F. 

52 Taubenfeld, Howard J., "National Weather Modification Policy Act of 1976 ; Interna- 
tional Agreements." Background paper for use of the U.S. Department of Commerce 
Weather Modification Advisory Board, March 1977, p. 13. 

53 See table 1, ch. 9, p. 409. 

54 These activities and other international aspects of weather modification are discussed 
in ch. 10. 

55 See previous section on legal issues, p. 17. 


United States at the expense of other countries or that such activities 
have resulted in damage to the environment in those countries. 56 

5. As in domestic research projects, there are allegations of insuffi- 
cient funding over periods of time too short to achieve significant 
results in the case of internationally sponsored experiments; in par- 
ticular, many scientists feel that a means should be devised to insure 
that the planned Precipitation Enhancement Project (PEP) receives 
adequate continuous support. 

6. Other nations should be consulted with regard to any planned 
weather modification activities by the United States which might con- 
ceivably affect, or be perceived to affect, those countries. 


The body of research on ecological effects of weather modification 
is limited but significantly greater than it was a decade ago. It is 
still true that much remains unknown about ecological effects of 
changes to weather and climate. 

Economically significant weather modification will always have an 
eventual ecological effect, although appearance of that effect may be 
hidden or delayed by system resilience and/or confused by system 
complexity. It may never be possible to predict well the ecological 
effects of weather modification; however, the more precisely the 
weather modifier can specify the effects his activities will produce in 
terms of average percentage change in precipitation (or other vari- 
ables), expected seasonal distribution of the induced change, expected 
year-to-year distribution of the change, and changes in relative form 
of precipitation, the more precise can be the ecologist's prediction of 
possible ecological effects. 

Ecological effects will result from moderate weather-related shifts 
in rates of reproduction, growth, and mortality of plants and animals; 
they will rarely be sudden or catastrophic. Accordingly, weather modi- 
fied ions which occur with regularly over time are the ones to which 
biological communities will react. Adjustments of plant and animal 
communities will usually occur more slowly in regions of highly vari- 
able weather than in those with more uniform conditions. Deliberate 
weather modification is likely to have greater ecological impact in 
semiarid systems and less impact in humid ones. Since precipitation 
augmentation, for example, would have the greatest potential for eco- 
nomic value and is, therefore, likely to have its greatest potential ap- 
plication in such areas, the ecological impacts in transition areas will 
be of particular concern. 

Although widespread cloud seeding could result in local, temporary 
increases in concentrations of silver (from the most commonly used 
seeding agent, silver iodide), approaching the natural quantities in 
surface waters, the exchange rates would probably be an order of 
magnitude Lower than the natural rates. Even in localized areas of 
precipital ion management, it appears I hat exchange rates will be many 
orders of magnitude smaller than those adversely affecting plants and 
soils. Further research is required, however, especially as other poten- 
tial seeding agents are introduced. 

m p or example tbere were charges that attempts to mitigate severe effects of Hurricane 
Fifl in 15>75 caused devastat ion to Honduras. :i charge which the United Nt;ites officially 
denied, since no hurricanes had been seeded under Project Stormfury since 1971. 



(By Robert E. Morrison, Specialist in Earth Sciences, Science Policy Research 
Division, Congressional Research Service) 


The history of the desire to control the weather can be traced to 
antiquity. Throughout the ages man has sought to alleviate droughts or 
to allay other severe weather conditions which have adversely affected 
him by means of magic, supplication, pseudoscientific procedures such 
as creating noises, and the more on less scientifically based techniques 
of recent times. 

The expansion in research and operational weather modification 
projects has increased dramatically since World War II; nevertheless, 
activities predating this period are of interest and have also provided 
the roots for many of the developments of the "modern" period. In a 
1966 reprt for the Congress on weather modification, Lawton Hart- 
man stated three reasons why a review of the history of the subject 
can be valuable: (1) Weather modification is considerably older than 
is commonly recognized, and failure to consider this fact can lead to a 
distorted view of current problems and progress. (2) Weather modi- 
fication has not developed as an isolated and independent field of re- 
search, but for over a century has been parallel to and related to 
progress in understanding weather processes generally. (3) Earlier 
experiences in weather modification may not have been very different 
from contemporary experiences in such matters as experimental de- 
sign, evaluation of results, partially successful projects, and efforts to 
base experiments on established scientific principles. 1 

Hartman found that the history of weather modification can be 
conveniently divided into five partially overlapping periods. 2 He refers 
to these as (1) a prescientific period (prior to about 1839); (2) an 
early scientific period (extending approximately from 1839 through 
1891) ; (3) a period during which elements of the scientific framework 
were established (from about 1875 to 1933) ; (4) the period of the 
early cloud-seeding experiments (1921 to 1946) ; and (5) the modern 
period, beginning with the work of Langmuir, Schaefer, and Vonne- 
gut (since 1946). This same organization is adopted in discussions 
below ; however, the four earlier periods are collected into one section, 
while the more significant history of the extensive activities of the 
post-1946 period are treated separately. 

1 Hartman, Lawton M., "History of Weather Modification. " In U.S. Congress, Senate 
Committee on Commerce "Weather Modification and Control." Washington. D.C U.S. 
Government Printing Oflice, 1966 (89th Cong., 2d sess.. Senate Rept. No. 1139: prepared 
by the Legislative Reference Service, the Library of Congress, at the request of Warren G. 
Maemn«on) , p. 11. 

2 Ibid. 



History or Weather Modification Prior to 1946 


From ancient times through the early 19th century, and even since, 
there have been reported observations which led many to believe that 
rainfall could be induced from such phenomena as great noises and 
extensive fires. Plutarch is reported to have stated, "It is a matter of 
current observation that extraordinary rains pretty generally fall 
after great battles/' 3 Following the invention of gunpowder, the fre- 
quency of such claims and the conviction of those espousing this 
hypothesis increased greatly. Many cases were cited where rain fell 
shortly after large battles, A practical use of this phenomenon was re- 
ported to have occurred in the memoirs of Benvenuto Cellini when, in 
1539 on the occasion of a procession in Rome, he averted an impending 
rainstorm by firing artillery in the direction of the clouds, "which had 
already begun to drop their moisture." 4 

William Humphreys jDOsed a plausible explanation for the appar- 
ently high correlation between such weather events and preceding 
battles. He noted that plans were usually made and battles fought in 
good weather, so that after the battle in the temperate regions of 
Europe or North America, rain will often occur in accordance with 
the natural 3- to 5-day periodicity for such events. 5 Even in modern 
times there was the conviction that local and global weather had been 
adversely affected after the explosion of the first nuclear weapons and 
the various subsequent tests in the Pacific and elsewhere. Despite 
statements of the U.S. Weather Bureau and others pointing out the 
fallacious reasoning, such notions became widespread and persistent. 7 

In addition to these somewhat rational though unscientific obser- 
vations, many of which were accompanied by testimony of reliable 
witnesses, there had been, and there still exist in some primitive cul- 
tures, superstitions and magical practices that accompany weather 
phenomena and attempts to induce changes to the weather. Daniel 
Halacy relates a number of such superstitiouslike procedures which 
have been invoked in attempts to bring rain to crops during a drought 
or to change the 1 weather in some other way so as to be of particular 
benefit to man : 8 

Primitive rainmakers would often use various intuitive gestures, such as 
sprinkling water on the soil that they wanted the heavens to douse, Mowing 
mouthfuls of water into the air like rain or mist, hammering on drums to inu- 
la re thunder, or throwing firebrands into the air to simulate lightning. 

Women would carry water at night to the field and pour it out to coax the 
skies to do likewise. 

American Indians blew water from special pipes in imitation of the rainfall. 

It was believed that frogs came down in the rain because many were seen 
following rain : therefore, frogs were hung from trees so that the heavens would 
pour down rain upon them. 

Sometimes children were buried up to their necks in the parched ground and 
then cried for rain, their tears providing the imitative magic. 

Ward, R. !>«• <\. "Artificial Rain : a Review of the Subject to the Close of lSSft." Amor- 
lean Meteorological Journal; vol. s. May 1891-Aprtl *S92, p. 484. 
* Ibid., n. 408. 

s Humphreys. William -1 . "Rain Making and Other Weather Vagaries." Baltimore, The 
Williams and Wilkins Co.. 11*20. p. 31, 

"Byers, Horace i:.. 'History of Weather Modification." In Wilnot N. Hess (editor), 
"Weather and Climate Modification," New York. Wiley, 1!)74, p. 4. 
~ T'.id 

« Halacy, Daniel S., Jr., "The Weather Changers," New York. Harper & Row. 1908. pp. 


In China, huge paper dragons were part of religious festivals to bring rain; 
if- drought persisted, the dragon was angrily torn to bits. 

North American Indians roasted young women from enemy tribes over a slow 
fire, then killed them with arrows before eating their hearts and burying their 
remains in the fields they wanted irrigated with rainfall. 

Scottish witches conjured up the wind by beating a stone three times with a 
rag dipped in water, among intonations like those of characters in a Shake- 
spearean play. 

New Guinea natives used wind stones upon which they tapped with a stick, 
the force of the blow bringing anything from a zephyr to a hurricane. 

Pregnant women in Greenland were thought to be able to go outdoors, take a 
breath, and exhale it indoors to calm a storm. 

In Scandinavian countries witches sold knotted bits of string and cloth which, 
supposedly, contained the wind ; untying one knot at sea would produce a mod- 
erate wind, two a gale, and three a violent storm. 

Australian bushmen thought that they could delay the Sun by putting a clod 
of dirt in the fork of a tree at just the height of the Sun, or hasten its departure 
by blowing sand after it. 

Bells have been thought to prevent hail, lightning, and windstorms, and some- 
times they are still rung today for this purpose. 


James P. Espy was a 19th century American meteorologist known 
especially for his development of a theon^ of storms based on convec- 
tion. Recognizing that a necessary condition for rainfall is the 
formation of clouds by condensation of water vapor from rising air, 
Espy considered that rain could well be induced artificially when air 
is forced to rise as a result of great fires, reviving a belief of the pre- 
.scientific era but using scientific rationale. In the National Gazette in 
Philadelphia of April 5, 1839, he said : 

From principles here established by experiment, and afterward confirmed by 
observation, it follows, that if a large body of air is made to ascend in a column, 
a large cloud will be generated and that that cloud will contain in itself a self- 
sustaining power, which may move from the place over which it was formed, and 
cause the air over which it passes, to rise up into it, and thus form more cloud 
and rain, until the rain may become more general. 8 

If these principles are just, when the air is in a favorable state, the bursting 
out of a volcano ought to produce rain ; and such is known to be the fact ; and 
I have abundant documents in my possession to prove it. 

So, under very favorable conditions, the bursting out of great fires ought to 
produce rain ; and I have many facts in my possession rendering it highly 
probable, if not certain, that great rains have sometimes been produced by great 
fires. 10 

Later in the same article Espy stated that : 

From these remarkable facts above, I think it will be acknowledged that there 
is some connection between great fires and rains other than mere coincidence. 
But now. when it is demonstrated by the most decisive evidence, the evidence 
of experiment, that air, in ascending into the atmosphere in a column, as it must 
do over a great fire, will cool by diminished pressure, so much that it will begin 
to condense its vapor into cloud. 11 

Espy postulated three mechanisms which could prevent great fires 
from providing rain at all times when they occur: (1) If there is a 
current of air at some height, it sweeps away the uprushing current 
of air; (2) the dew-point may be too low to produce rain at all: and 
(3) there may be an upper stratum of air so light that the rising 

9 Espy. Tames P.. "Artificial Rains." National Gazette. Philadelphia. Apr. 5, lSf!9. Re- 
printed in James P. Espy, "Philosophy of Storms," Boston. Little & Brown. 1841. pd. 

10 Ibid., p. 494. 

11 Ibid., p. 496. 


column may not be able to rise far enough into it to cause rain. 12 He 
proposed an experiment in which he would set fire to a "large mass 
of combustibles," which would be ready for the right circumstances 
and at a time of drought. He added : "Soon after the fire commences, 
I will expect to see clouds begin to form * * *. I will expect to see 
this cloud rapidly increase in size, if its top is not swept off by a 
current of air at a considerable distance abov^e the Earth, until it 
becomes so lofty as to rain.'- 13 

For over a decade Espy served as an adviser to the Congress on 
meteorological problems. He proposed in 1850 what is perhaps the first 
Fedora! project for large-scale weather modification. His plan included 
amassing large quantities of timber in the Western States along a 
600- to 700-mile north-south line, to be set on fire simultaneously at 
regular T-day intervals. He believed that this fire could have started 
a "rain of great length" traveling toward the East, not breaking up 
until reaching "far over the Atlantic Ocean; that it will rain over 
the whole country east^of the place of beginning." The cost of this 
experiment would "not amount to half a cent a year to each individual 
in the United States." 14 Congress did not endorse the proposal for 
reasons which are unknown: however. Fleagle speculates that perhaps 
this failure was due to the fact that Congress had not yet accustomed 
itself to appropriating funds for scientific enterprises. 15 

There was continuing controversy over whether or not fire could 
cause increased rainfall. In an article which appeared in Nature in 
1871, J. K. Laughton stated that, "The idea that large fires do, in some 
way, bring on rain, is very old; but it was, I believe, for the first time 
stated as a fact and explained on scientific grounds by the late Pro- 
fessor Espy." 10 Laughton cited instances where burning brush in hot, 
dry weather did not result in any rainfall, and he concluded that : 

Large fires, explosions, battles, and earthquakes do tend to cause atmospheric 
disturbance, and especially to induce a fall of rain ; but that for the tendency to 
produce effect, it is necessary that other conditions should be suitable. With 
regard to storms said to have been caused by some of these agencies, the evidence 
is still more unsatisfactory ; and, in our present ignorance of the cause of storms 
generally, is quite insufficient to compel us to attribute any one particular gale, 
extending probably over a wide area, to some very limited and comparatively 
insignificant disturbance. 17 

The 1871 Chicago fire also aroused interest, many believing that the 
fire was stopped by the rainfall which it had initiated. Ward cites a 
telegram of the time sent to London which read : 

This fire was chiefly checked on the third or fourth day by the heavy and con- 
tinuous downpour of rain, which it is conjectured is partly due to the great atmos- 
pheric disturbances which such an extensive lire would cause, especially wben we 
are told that the season just previous to the outbreak of the fire had been par- 
ticularly dry." 

u Ibid. 

1 ■ I 'id., p. 400. 

« Espy, James P., "Second Reporl on Meteorology to the Secretary of the Navy." U.S. 
Senate. Executive Doctlmetats; No. 89, vol. 11, ."{1st Cong., 1st Bess. Washington, Wm. M 
Belt 1850. p. 20. 

us Fleagle. Robert O.. "Background and Present status of Weather Modification." In 
Robert (i. Flea pie (editor). "Weather Modification: Science and Public Policy." University 
of w ah inert on Press, Seattle 1968, p. 7. 

"' Lautrhton. J K., "Can Weather lie Influenced bv Artificial Means?" Nature, Feb. 10. 
1871 i. :•(»(; 

17 Ibid., p. 307. 

« Reported in Ward. "Artificial Rain : a Review of the Subject to the Close of 1889," 1*02. 
pp. 480-400. 


On the other hand, Prof. I. A. Lapham, speaking of the Chicago fire, 
contradicted the previous account, saying : 

During all this time — 24 hours of conflagration — no rain was seen to fall, nor 
did any rain fall until 4 o'clock the next morning ; and this was not a very con- 
siderable downpour, but only a gentle rain, that extended over a large district of 
country, differing in no respect from the usual rains. It was not until 4 days 
afterward that anything like a heavy rain occurred. It is, therefore, quite certain 
that this case cannot be referred to as an example of the production of rain by a 
great fire. 19 

Lapham goes on to say that, "The case neither confirms nor dis- 
proves the Espian theory, and we may still believe the well-authenti- 
cated cases where, under favorable circumstances of very moist air and 
absence of wind, rain has been produced by very large fires." 20 

Prof. John Trowbridge of Harvard reported in 1872 on his experi- 
ments in which he investigated the influence of flares on atmospheric 
electricity. Noting that the normal atmospheric state is positive and 
that clearing weather is often preceded by a change from negative to 
positive charge, he suggested that perhaps large fires may influence the 
production of rain by changing the electrical state of the atmosphere, 
since, in his tests, his flame tended "to reduce the positive charge of 
electricity which generally characterizes the air of fine weather." 21 He 
concluded by saying: "The state of our knowledge, however, in regard 
to the part that electricity plays in atmospheric changes is very meager. 
The question of the truth of the popular belief that great fires are fol- 
lowed by rain still remains unanswered." 22 

Meanwhile, H. C. Russel, president of the Royal Society of South 
Wales and government astronomer, attempted to dispel the ideas that 
both cannonading and great fires could be used to produce rain. He 
hypothesized that, if fire were to have such an effect, rain should arrive 
within 48 hours following the fire. Reviewing the records of 42 large 
fires (including two explosions) covering a 21-year period, Russel 
concluded that there was not one instance in which rain followed 
within 48 hours as an evident consequence of the fire. He further cal- 
culated that to get increased rainfall of 60 percent over a land surface 
of 52,000 square feet at Sidney would require 9 million tons of coal per 
day, in an effort to show what magnitude of energy expenditure was 
necessary and how futile such an attempt would be. 23 

Toward the latter part of the 19th century there were a number of 
ideas and devices invented for producing rain artificially. In 1880 
David Ruggles of Virginia patented what he said was "a new and use- 
ful mode of producing rain or precipitating rainfalls from rainclouds, 
for the purpose of sustaining vegetation and for sanitary purposes." 
His plan included a scheme by which balloons carrying explosives were 
sent up into the air, the explosives to be detonated in the upper air "by 
electric currents." 24 

19 Lanham, I. A.. "The Great Fires of 1871 in the Northwest." The Journal of the Frank- 
lin Institute, vol. 64, No. 1. July 1872, pp. 46-47. 

20 IMd., p. 47. 

21 Trowlirirtge, John, "Great Fires and Rain-storms." The Popular Science Monthly, vol. 2, 
December 1872. p. 211. 

22 Tbid. 

23 Report of an address bv H. C. Russel was given in Science, vol. 3, No. 55, Feb. 22. 1884, 
pp. 229-230. 

24 "New Method of Precipitating Rain Falls," Scientific American, vol. 43, Aug. 14. 1S80, 
p. 106. 


G. H. Bell suggested a rainmaking device, consisting of a hollow 
tower 1.500 feet high, through which air was to be blown into the 
atmosphere, the volume of the up-rushing air to be increased through 
use of a s}^stem of tubes around the tower. The inventer consider that 
the same system could be used to prevent rain, by reversing the blower 
so that the descending air might "annihilate" the clouds. 25 

Still other schemes and contrivances were proposed and patented. 
J. B. Atwater was granted a patent in 1887 for a scheme to dissipate 
tornadoes by detonating an explosive charge in their centers, and an- 
other was granted to Louis Gathman in 1891 for seeding clouds for rain 
by exploding a shell containing "liquid carbonic acid gas" at cloud 
height, 20 the latter concept antedating by over 50 years the more recent 
carbon dioxide seeding projects. 

There continued to be adherents to the idea that explosions could 
cause rainfall. This belief was reinforced by "evidence" of such a con- 
nection in a book by Edward Powers, called "War and the Weather," 
published in 1871 and 1890 editions, in which the author recounted the 
instances in which rain followed battles, mostly from North America 
and Europe during the 19th century. 27 

Powers was convinced that : 

The idea that rain can be produced by human agency, though sufficiently 
startling, is not one which, in this age of progress, ought to be considered as 
impossible of practical realization. Aside from its connection with the supersti- 
tions of certain savage tribes, it is an opinion of comparatively recent origin, and 
is one which cannot be regarded as belonging, in any degree, to a certain class of 
notions which prevail among the unthinking; * * * on the contrary, it is one 
which is confined principally to those who are accustomed to draw conclusions 
only from adequate premises, and * * * founded on facts which have come under 
their own observation. 28 

In tones somewhat reminding us of those urging a greater Federal 
research effort in recent years, Powers proposed that experiments be 
undertaken for economic benefit : 

Judging from the letters which I have received since commencing in 1870 an 
attempt to bring forward the subject of rains produced by cannon tiring. I believe 
that the country would regard with interest some experiments in the matter, and 
would not begrudge the expense, even if they should prove unsuccessful in leading 
to a practical use of the principle under discussion. In some matters connected 
w T ith science, the Government has justly considered that an expenditure of public 
funds was calculated to be of public benefit: but where, in anything of tiie kind 
it. has ever undertaken, has there been so promising a field for such actions as 
here? 20 

Powers, upon examining the records of many battles, said : 

Let us proceed to facts — facts not one of which, perhaps, would be of a in- 
significance if it stood alone and unsupported by the others; but which, taken 
in the aggregate, furnish the strongest evidence that heavy artillery firing 
has an influence on the weather and tends to bring rain. 11 

Perhaps influenced by the arguments of Powers and others, in 
1890 the U.S. Congress had become so much interested in and gained 

Another Ka in Controller." Scientific American, vol. 4:{. Aug, 21. 1SSO. p 11M. 

26 Harrington, Mark W.. "Weather-making, Ancient and Modern," Smithsonian Institu- 
tion Annual Report, to July 1894, pp. 249 1270. 

-'■ I'owers. IMward. "War and the Weather." Delavan. Wis.. 10. Powers. 1890, revised 
edition, 202 pp. (An earlier edition was published in Chicago in 1871. Incidentally, the 
plates for the first edition were deal roved in the Chicago lire, and I'owers did not have an 
opportunity to complete his revision until 1890. ) 

-* Ihid.. p. 5. 

■ Ihid.. p. 143. 

* Ihid., p. 11. 


such faith in the possibility of weather modification that funds 
we re appropriated to support experiments to be carried out under 
the auspices of the Forestry Division of the U.S. Department of 
Agriculture. The initial $2 ? 0p0 appropriated was increased first to 
$7,000, and finally to $10,000. in the first federally sponsored weather 
modification project. Of the total appropriated. $9,000 was to be 
spent on held experiments. Gen. Robert St. George Dyrenforth was 
selected by the Department of Agriculture to direct these tests, hav- 
ing earlier conducted tests near Utiea, X.Y., and Washington, D.C.. 
using balloons and rockets carrying explosives. The principal ex- 
periments were executed near Midland, Tex., using a variety of ex- 
plosive devices, detonated singly and in volleys, both on the ground 
and in the air. 31 

According to an interesting account by Samuel Hopkins Adam-. 
Dyrenforth arrived in Texas on a hot day in August 1891 with a 
company of 80 workers, including "* * * chemists, weather observers, 
balloon operators, electricians, kitefiiers, gunners, minelayers, sap- 
pers, engineers, and laborers * * * together with some disinterested 
scientists, who were to serve as reporters." 32 Adams discusses the ap- 
paratus which Dyrenforth took with him : 

The expedition's equipment was impressive. There were 68 balloons of from 10 
to 12 feet in diameter, and one of 20 feet — all to be hlled with an explosive mixture 
of hydrogen and oxygen. There were also sixty 6-inch mortars, made of pipe, and 
several tons of rackarock (a terrifying blend of potassium chlorate and nitro- 
benzol that, was the general's favorite "explodent" >, dynamite, and blasting 
powder. Finally, there were the makings of a hundred kites, to be assembled on the 
scene, and sent up with sticks of dynamite lashed to them. The congressional 
$9,000 fell considerably short of sufficing for so elaborate an outfit, but expectant 
Texans chipped in with liberal contributions and the railroads helped out by sup- 
plying free transportation. 1 " 

Dyrenforth carried out five series of trials during 1891 and 1892 : 
one period of sustained cannonading coincided with a heavy down- 
pour, and the apparent connection provided support to the credi- 
bility of many people, who accepted the hypotheses as confirmed. 
Dyrenforth gave optimistic and promising reports of his results: 
however, meterologists and other scientists were critical of his work. 
It does not appear that the Forestry Division was fervently ad- 
vocating the research program for which it had responsibility. In 
1891, Bernhard E. Fernow, Chief of the Division of Forestry, re- 
ported to the Secretary of Agriculture his sentiments regarding the 
experiments which were to be conducted in the coming summer, with 
a caution reminiscent of the concerns of many meterologists of the 
1970°s : 

The theories in regard to the causes of storms, and especially their local and 
temporal distribution, are still incomplete and unsatisfactory. It can by no means 
be claimed that we know all the causes, much less their precise action in precipi- 
tation. It would, therefore, be presumptuous to deny any possible effects of ex- 
plosions ; but so far as we now understand the forces and methods in precipitating 
rain, there seems to be no reasonable ground for the expectation that they will be 
effective. We may say, then, that at this stage of meteorological knowledge we 
are not justified in expecting any results from trials as proposed for the predtre- 
tion of artificial rainfall, and that it were better to increase this knowledge first 

31 Fleagle. "Background and Present Status of Weather Modification." 1968, pp. 7-8. 

32 Adams. Samuel Hopkins. The New Yorker. Oct. 9, 1952, pp. 93-100. 
*> Ibid., i«. !.'4. 


by simple laboratory investigations and experiments preliminary to experiment 
on a larger scale. 34 

In 1893, the Secretary of Agriculture asked for no more public funds 
for support of this project. 35 

Fleagle tells about the use of 36 "hail cannons" by Albert Stiger, a 
town burgomaster, on the hills surrounding his district in Austria in 

Tbe hail cannon consisted of a vertically pointing three-centimeter mortar 
above which was suspended the smokestack of a steam locomotive. This device 
not only produced an appalling sound, but also created a smoke ring a meter or 
more in diameter which ascended at about one hundred feet per second and 
produced a singing note lasting about ten seconds. Initial successes were impres- 
sive, and the hail cannon was widely and rapidly copied throughout central 
Europe. Accidental injuries and deaths were numerous, and in 1902 an inter ua- 
tional conference was called by the Austrian government to assess the effects of 
the hail cannon. The conference proposed two tests, one in Austria and one in 
Italy, the results of which thoroughly discredited the device. 36 

Though unsuccessful, the work of Dyrenforth and others had in- 
spired belief in the possibilities of drought alleviation such that a 
number of unscrupulous "rainmakers" were able to capitalize on the 
situation. Halacy gives an account of a famous rainmaker of the early 
20th century, Charles Warren Hatfield, who operated for about 10 
years in the western United States. With a 25-foot platform and a 
secret device for dispensing chemicals, he claimed to create rain over 
extensive areas. In 1916. Hatfield contracted with the city of San Diego 
to alleviate drought conditions and was to be paid $1,000 for each inch 
of rain produced. When 20 inches of rain coincidentally fell nearby, 
the resulting floods destroyed a dam, killed 17 people, and produced 
millions of dollars damage. Hatfield, faced with a choice of assuming 
financial responsibility for the lawsuits or leaving the city without pay, 
chose the latter. 37 

One of Hatfield's accomplices was a colorful racetrack reporter from 
Xew York, who met and joined Hatfield in California in 1912, named 
James Stuart Aloysius MacDonald, alias Colonel Stingo, "the Honest 
Rainmaker." Over his half -century career as a writer, mostly for var- 
ious horseracing journals. MacDonald reportedly involved himself in 
various schemes for quick profit, including weather changing projects 
on both the west and east coasts. Contracts with clients were drawn up 
with terms for remuneration that resembled very much the language 
of success or failure at the racetrack. By his own admission, Mac- 
Donald based his odds for success on past weather data for a given 
area, which he obtained from records of the U.S. Weather Bureau or 
the Xew York Public Library. 88 MacDonald, or Colonel Stingo, was 
the inspiration for a Broadway play called "The Rainmaker" which 
opened in 1954. 


Espy's L839 proposal for an experiment on the production of con- 
vection currents and water vapor condensation at high altitudes was 

■ A Fernow, Rernhard E.. in report to Jeremiah McClain Rusk. Secretary of Agriculture, 
1891, an reported in Ward, "Artificial Rain ; a Review of the Subject to the Close of 1889." 
1882. p. 492. 

• livers. "History of Weather .Modification." 1 1*74. p. 5. 
38 Fleajcle. "Rackpronnd and Present Status of Weather Modification," 1968, p. 9. 
:t7 Halacy, "The Weather Changers," 1968, pp. 68 69. 
38 Liebling, A. J., "Profiles," The New Yorker, Sept. 20, 1902, pp. 43-71. 


based on sound physical principles. Since knowledge of atmospheric 
processes was expanding and unfolding rapidly at the time, Hartman 
reminds us that the limited usefulness of Espy's weather modification 
concepts should not be ascribed to faulty logic, but rather to the primi- 
tive understanding at the time of the complex processes in precipita- 
tion, many of which are still not understood satisfactorily. 39 

The understanding which meteorologists have today about precipi- 
tation has been learned slowly and sometimes painfull}^, and, while 
many of the discoveries haA'e resulted from 20th century research, 
some important findings of the latter part of the 19th century are 
fundamental to these processes. Important results were discovered in 
1875 by Coulier in France on foreign contaminant particles in the 
normal atmosphere, and quantitative measurements of the concentra- 
tions of these particles were achieved by Aitken in 1879. These events 
established a basis for explaining the fundamental possibility for 
occurrence of precipitation. Earlier, it had been learned that high 
supersaturations were required for the formation of water droplets. 40 
Aitken was the first to imply that there are two types of nuclei, those 
with an affinity for water vapor (hygroscopic particles) and nuclei 
that require some degree of supersaturation in order to serve as con- 
densation centers. The Swedish chemist-meteorologists of the 1920's 
developed a theory of condensation on hygroscopic nuclei and showed 
the importance of sea-salt particles. In the 1930's in Germany and the 
United Kingdom, a series of measurements were conducted on the 
numbers and sizes of condensation nuclei by Landsberg, Judge, and 
Wright. Data from measurements near Frankfurt, augmented sub- 
sequently by results from other parts of the world, have been adopted 
as the standard of reference for condensation nuclei worldwide. 41 

At the beginning of the 1930's important aspects of cloud phys' 
were not yet understood. In particular, the importance of thp ic ,ri phu 
to precipitation was not yet clarified, though, ever since the turn of 
the century meteorologists were aware that water droplets were abun- 
dantly present in clouds whose temperatures were well below the freez- 
ing point. Little was known about the microphysics of nucleation of ice 
crystals in clouds ; however, it had been noted that rains fell only after 
visible glaeiation of the upper parts of the clouds. Understanding 
of these processes was essential before scientific seeding of clouds for 
weather modification could be pursued rationally. In 1933 Tor Berg-er- 
on presented and promulgated his now famous theory on the initiation 
of precipitation in clouds containing a mixture of liquid and ice. 
W. Findeisen expanded on Bergeron's ideas and published a clearer 
statement of the theory in 1938 ; consequently, the concept is generally 
known as the Bergeron-Findeisen theory. 42 in his investigation of the 
formation of ice crystals, Findeisen was of the opinion that they crys- 
talled directly from the vapor (that is, by sublimation) rather than 
freezing from droplets. He also conjectured that quartz crystals might 
be the nuclei responsible for this process and even foresaw that the 
mechanism might be initiated artificially by introducing suitable 
nuclei. 43 

33 Hartman, "Weather Modification and Control," 1966, p. 13. 

40 Ibid. 

41 Bvers. "History of Weather Modification," 1974, p. 7. 

42 Ibid., p. 8. 

*» Ibid., pp. 8-9. 

34-857—79 5 


Findeisen stated emphatically that rain of any importance must 
originate in the form of snow or hail, though Bergeron had admitted 
the occurrence of warm rain in the tropics. Though many meteorolo- 
gists doubted that the ice crystal process was an absolute requirement 
for rain, they had been unable to collect evidence from aircraft obser- 
vations. In Germany aerological evidence was obtained on the growth 
of rain drops by the collision-coalescence process in "warm" clouds, 
but the papers on this work were published in 1940, and World War 
II restricted communication of the results to meteorologists world- 
wide. Meanwhile in the United States, papers were published on the 
theory of the warm rain process. In 1938, Houghton showed that pre- 
cipitation could be started by either the Bergeron process or by the 
collision-coalescence process. He noted that drops could be formed by 
condensation on "giant" hygroscopic nuclei present in the air and that 
growth of droplets to raindrop size was possible through collision. 
G. C Simpson elucidated further on condensation and precipitation 
processes in 1941, disagreeing with Findeiseivs rejection of "warm" 
rain formation by the collision-coalescence process. 44 


Starting about 1920 and continuing for about two decades until 
the outbreak of World War II, there were a number of experiments 
and operations intended to produce rain or modify the weather in 
some other way. Although some of these activities were pusued in a 
scientific manner, others were less so and were directed at producing 
immediate results; all of these projects lacked the benefit of the funda- 
mental knowledge of precipitation processes that was to be gained 
later during this same period, the discoveries of which are discussed 
in the preceding subsection. Various schemes during this period in- 
cluded the dispensing of materials such as dust, electrified sand, dry 
ice, liquid air, and various chemicals, and even the old idea that explo- 
sions can bring rain. Field tests were conducted in the United States, 
Germany, the Netherlands^ and the Soviet Union. 

Byers tells .about the experimental work of Dr. E. Leon Chaffee, 
professor of physics at Harvard, who became interested in the possi- 
bility of making cloud particles coalesce by sprinkling electrically 
charged sand over the clouds : 

Dr. Chaffee became enthusiastic about the idea and developed in his laboratory 
a nozzle tor charging sand and dispersing it from an airplane. The nozzle could 
deliver sand grains having surface gradients of the order of 1.000 V/ein. Flight 
experiments were carried out in August and Seprcmber of 1024 at Aberdeen, 
Md.. with an airplane scattering the sand particles in the clear air above clouds 
having tops at to 10,000 feet. Dr. Chaffee reported "success*' in the reverse 
sense, in that several clouds were observed to dissipate after treatment. The tests 
were well publicized in newspapers and scientific news journals, and this author, 
then a freshman at the University of California, recalls that his physics pro- 
fessors were enthusiastic about the idea. Chaffee's results probably would not 
endure the type of statistical scrutiny to which experiments of this kind are 
subject today. 43 

Chaffee considered several trials successful, since clouds were dis- 
sipated after being sprayed with the charged sand. It has been pointed 

" Ibid . p. 9. 
« Ibid., p. 5. 


out, however, in view of the much greater experience in recent years, 
that scientists must be extremely cautious in ascribing success in such 
experiments, when the evidence is based largely on visual obser- 
vations. 4 ' 1 

In the Netherlands, August Veraart successfully produced rain by 
seeding clouds with dry ice from a small aircraft in 1930. This was 
16 years before the work at General Electric in the United States, when 
clouds were also seeded with dry ice, initiating the modern period in 
the history of weather modification. Since Veraart probably did not 
understand the mechanism involved in the precipitation process which 
he triggered, ho did not realize that the dry ice was effective in develop- 
ment of ice crystals by cooling supercooled clouds, and his success was 
likely only a coincidence. Byers observes that Veraart's vague con- 
cepts on changing the thermal structure of clouds, modifying tem- 
perature inversions, and creating electrical effects were not accepted, 
however, by the scientific community. 47 He claimed to be a true rain- 
maker and made wide, sweeping claims of his successes. He died in 
19o*2, a year before Bergeron's theory appeared, not aware of the theo- 
retical basis for his work. 48 

Partly successful experiments on the dissipation of fog were con- 
ducted by the Massachusetts Institute of Technology in the 1930s, 
under the direction of Henry G. Houghton. At an airfield near Round 
Hill, Mass., fog was cleared using sprays of water-absorbing solutions, 
particularly calcium chloride, as well as fine particles of dry hygro- 
scopic material. Results of these experiments, which predated some of 
the present-day foo- dispersal attempts bv some 30 vears, were reported 
in 1938. 19 

Weather Modification Sixce 1946 


The following chronology of "critical events" relating to weather 
modification policy, compiled by Fleagle. unfolds only some of the 
major events and activity periods which have occurred since the his- 
toric discoveries of 1946 : 50 

1946 : Schaefer demonstrated seeding: with dry ice. 

1947 : Vonnegut demonstrated seeding with silver iodide. 

1947-55 : Irving Langmuir advertised weather modifieaton widely and aggres- 

1947- 53: General Electric field experiments ("Cirrus") extended evidence 
that clouds can he deliherately modified, but failed to demonstrate large effects. 

1948- 50: Weather Bureau Cloud Physics Project on cumulus and stratiform 
clouds resulted in conservative estimate of effects. 

1948-52 : Commercial operations grew to cover 10 percent of United States. 

1950: Report of Panel on Meteorology of Defense Department's Research and 
Development Board (Haurwitz, Chairman) was adverse to Langmuir's claims. 

1953: Public Law 83-256 established President's Advisory Committee on 
Weather Control. 

45 McDonald. James E.. "An Historical Note on an Early Cloud-Modification Experiment. 
Bulletin of the American Meteorological Society, vol. 42. No. 3, March 1961, p. 19o. 

47 Byers. "History of Weather Modification." 1947. p. 6. 

48 Hartman. "Weather Modification and Control." 1966. p. 15. , , „ 

» Houghton. Henrr G.. and W. H. Radford. "On the Local Dissipation of Natural bog. 
Papers in Physical Oceanography and Meteorology. Massachusetts Institute of Technology 
and Woods Hole Oceanographic Institution, vol. 6, No. 3. Cambridge and Woods Hole, Mass., 
October 1938, 63 pp. , „ - .. „ „ . 

50 Fleagle. Robert G . "An Analysis of Federal Policies in \\ eather Modification. Back- 
ground paper prepared for use by the U.S. Department of Commerce Weather Modification 
Advisory Board. Seattle. Wash., March 1977. pp. 3-5. 


1953-54: "Petterssen" Advisory Committee organized field tests on storm sys- 
tems, convective clouds, and cold and warm fog (supported by the Office of 
Naval Research, the Air Force, the Army Signal Corps, and the Weather 
Bureau). These statistically controlled experiments yielded results which have 
been substantially unchanged in subsequent tests. 

1957: Report of Advisory Committee (Orville, Chairman) concluded that tests 
showed 15 percent increase in orographic winter precipitation. 

1957 : Major cut in research support across the board by Defense Department 
sends major perturbation through research structure. 

195S: Public Law 85-510 assigned lead agency responsibility to the National 
Science Foundation (NSF). 

1959: Commercial operations had diminished to cover about one percent of 
the United States. 

1961 : First hurricane seeding under Project Stormfury. 

1961 : Bureau of Reclamation authorized by Congress to conduct research in 
weather modification. 

1961 : RAND report on weather modification emphasized complexity of atmos- 
pheric processes and interrelation of modification and prediction. 

1962-70: Randomized field experiments established magnitude of orographic 

1964: Preliminary report of National Academy of Sciences/Committee on 
Atmospheric Sciences (NAS/CAS) roused anger of private operators and stimu- 
lated the evaluation of operational data. 

1964-present : Department of the Interior pushed the case for operational seed- 
ing to augment water supplies. 

1966: NAS/CAS report 1S50 laid the basis for expanded Federal programs. 

1966 : Report of NSF Special Commission on Weather Modification and an NSF 
symposium called attention to social, economic, and legal aspects. 

1966: Interdepartmental Committee for Atmospheric Sciences (ICAS) report 
f Newell, Chairman) proposed expanded Federal support to $90 million by 1970. 

1966- 68 : Efforts of the Departments of Commerce and Interior to gain lead 
agency status were unsuccessful. 

1967: ICAS recommended that Commerce be designated as lead agency. 
1967: S. 2916, assigning lead agency responsibility to the Department of Com- 
merce : passed the Senate but did not become law. 

1967- 72 : Military operational programs conducted in Vietnam. 
1968: Public Law 90-407 removed the NSF mandate as lead agency. 
1968 : Detrimental effects of acid rain reported from Sweden. 

1969: Public Law 91-190 (National Environmental Policy Act) required im- 
pact statements. 

1970; Massachusetts Institute of Technology Study of Critical Environmental 
Problems called attention to inadvertent effects on climate. 

1970 : Stratospheric contamination by SST's suggested. 

1971 : Departments of Commerce and Interior carried out operational programs 
in Oklahoma and Florida. 

1971 : Public Law 92-205 required filing of reports of non-Federal weather 
modification activities with the Department of Commerce. 

1971 : International Study of Man's Impact on Climate raised this issue to inter- 
national level. 

1971 : NAS/CAS report on priorities for the 1970's emphasized need for atten- 
tion to management and policy problems of weather modification. 

1971: Federal Council for Science and Technology approved seven national 
projects under various lead agencies. 

1971-72: First technological assessments of weather modification projects are 
favorable to operational programs. 

1971-74 : Climate impact assessment program ( CTAP) of Department of Trans- 
portation indicates potentially serious consequences of large SST fleet but sug- 
gests ways to ameliorate the problem. 

1972: Failure of Soviet wheat crop and drought in Sahel emphasized critical 
need for understanding climate and the value of effective weather modification. 

1973: Weather modification budget reduced by impoundment from $25.4 million 
to $20.2 million. 

1973 : Five national projects deferred or terminated. 

1973: NAS/CAS report on weather and climate modification confirmed earlier 
conclusions and recommended lead agency status for NOAA. 


1974 : Stratospheric contamination by freon reported. 

1974 : Domestic Council organized panels in climate change and weather 

1974 : General Accounting Office report on weather modification criticized 
weather modification program and pointed to need for lead agency. 

1974 : Defense Department released information on operations in Vietnam. 

1974 : The United States and the U.S.S.R. agreed to a joint statement intended 
"to overcome the dangers of the use of environmental modification techniques for 
military purposes." 

1975 : World Meteorological Organization Executive Committee proposed cumu- 
lus experiment perhaps in Africa or Iran. 

1975 : Department of Transportation CIAP report indicated that a fleet of 500 
SST's would deplete ozone significantly, but suggested that cleaner engines could 
be developed. 

1976: Chinese disapproval resulted in abandoning plans for Stormfury in the 
western Pacific. 

1976 : Hearings held on three weather modification bills by Senate Commerce 

1976: The National Weather Modification Policy Act of 1976 (Public Law 94- 
859) enacted requiring study of weather modification. 

1977 : Exceptionally dry winter in the west stimulates State operational pro- 
grams intended to increase mountain snowpack. 

Since the completion of Fleagle's list above in March 1977, at least 
three other activities of equivalent significance ought to be noted : 

1977 : The U.S. Department of Commerce Weather Modification Advisory Board 
established in April 1977 and initiated a major study on a recommended national 
policy and Federal program of research in weather modification, in accordance 
with requirements to be fulfilled by the Secretary of Commerce under Public Law 
94-490, the National Weather Modification Policy Act of 1976. 

1977 : The United Nations General Assembly approved a treaty banning environ- 
mental modification activities for hostile purposes on May 18, 1977 ; and the treaty 
opened for signature by the member nations. 

1978 : The Report of the Commerce Department's Weather Modification Advi- 
sory Board transmitted through the Secretary of Commerce to the Congress. 

The history of the modern period of weather modification which 
follows is essentially that of the two decades following the monumental 
discoveries of 1946. An excellent account of the history of weather 
modification, which emphasizes this period, has been prepared by 
Byers. 51 This work has been very helpful in some of the material to 
follow and is referenced frequently. The late 1960's and the 1970's are 
so recent that events during this period are discussed in various sections 
of the report as ongoing activities or events leading to current activities 
in weather modification research programs, operations, and policy 
decisions rather than in this chapter as an integral part of an updated 
history of the subject. 


The modern era of scientific weather modification begaai in 1946, 
when a group of scientists at the General Electric Co. demonstrated 
that, through "seeding," a cloud of supercooled water droplets could 
be transformed into ice crystals and precipitation could be induced. 
These were not traditional meteorologists, though their leader. Dr. 
Irving Langmuir, was a famous physicist and Nobel laureate. He and 
his assistant, Vincent J. Schaefer, had been working for 3 years on 
cloud physics research, however, in which they were studying particle 
sizes, precipitation static, and icing. Their field research was carried on 

Byers, "History of Weather Modification," 1974, pp. 3-44. 


at the summit of Mt. Washington., X.H.. where they observed super- 
cooled clouds which often turned into snowstorms. 52 

In an attempt to simulate field conditions. Schaefer contrived a 
laboratory setup using a home freezer lined with black velvet, with a 
light mounted so as to illuminate ice crystals that might happen to 
form in the box. Breathing into the box, whose temperature was about 
— 23° C, produced fog but no ice crystals, even when various sub- 
stances — including sand, volcanic dust, sulfur, graphite, talc, and 
salt — were dropped in as possible sublimation nuclei. 53 On July 12. 
19-16, Schaefer wanted to lower the freezer temperature somewhat, so 
he inserted a large piece of dry ice. and. in an instant, the air was 
full of millions of ice crystals. He discovered that even the tiniest 
piece of dry ice produced the same etfect. In fact, dry ice had no 
direct effect on the supercooled cloud; producing an air temperature 
below - 39° C was critical. 54 

In his paper on the laboratory experiments, published in the No- 
vember 15, 1946. issues of^Science v Schaefer stated : 

It is planned to attempt in the near future a large-scale conversion of super- 
cooled clouds in the atmosphere to ice crystal clouds, by scattering small frag- 
ments of dry ice into the cloud from a plane. It is believed that such an opera- 
tion is practical and economically feasible and that extensive cloud systems can 
be modified in this way. 53 

Two days before the paper appeared, on Xovember 13, 1946, 
Schaefer made his historic flight, accomplishing man's first scientific 
seeding of a supercooled cloud, as he scattered three pounds of dry ice 
along a 3-mile line over a cloud to the east of Schenectady, X.Y. At 
14.000 feet the cloud temperature was —20° C. and in about § minutes 
after seeding the entire cloud turned into snow, which fell 2,000 feet 
before evaporating. 56 

Dr. Bernard Vonnegut had also worked on aircraft icing research 
and in 1946 at General Electric was pursuing a variety of nueleation 
problems ; but. after Schaefer's laboratory experiments, he again 
turned his attention to ice nueleation research. He discovered that 
silver iodide and lead iodide had crystal structures close to that of ice 
and were also insoluble in water, and after repeated initial failures, 
owing to impurities in the material, Vonnegut was able to produce ice 
crystals, using very pure silver iodide powder, at temperatures only a 
few degrees below freezing. Soon means were developed for generating 
silver iodide smokes, and man's first successful attempt at artificial 
nueleation of supercooled clouds was accomplished. 57 

Langmuir explained that dry ice could make ice crystals form by 
lowering the temperature to that required for natural nueleation on 
whatever might be present as nuclei, or even in the absence of all 
nuclei; however, the silver iodide provided a nucleus that was much 
more efficient than those occurring naturally. 58 

" Ibid., pp. 9-10. 

" Halacy, "The Weather Changers/' ions. pp. S2-S3. 

« langmuir. Irvinp. "The Growth of Particles in Smoke, and Clouds and the Production 
of Snow from Supercooled Clouds. Proceedings of the American Philosophical Society, vol. 
92, no. 3, July 1048, p. 182. ' , , _ , 

Schaefer, Vincent J.. "The Production of Ice Crystals in a Cloud of Supercooled Water 
Droplets.' - Science, vol. U>4. No. 2707. Nov. 15. 1946, p. 459. 

" Byers, "History of Weather Modification," 1074. p. 12. 

57 H>id . p. 13. 

M Langmuir, Irvine. "Cloud Seeding by Menus of Dry Ice. Silver Iodide, and Sodium 
Chloride." Transactions of the New York Academy of Sciences, ser. II, vol. 14. November 
1951, p. 40. 


Following Schaefer's successful flight of November 13, 1946, and in 
the months and immediate years thereafter, Langmuir was quoted in 
the popular press as being very optimistic in his predicted benefits 
from weather modification. In a 1948 paper he said that k> * * * it 
becomes apparent that important changes in the whole weather map 
can be brought about by events which are not at present being con- 
sidered by meteorologists." 59 His publications and informal statements 
of this character touched off years of arguments with professional 
meteorologists, by whom refutation was difficult in view of Langmuir s 
standing in the scientific community. His enthusiasm for discussing 
the potential extreme effects from weather control was unrestrained 
until his death in 1957. 60 


Project Cirrus 

Although the business of the General Electric Co. had not been in 
meteorology, it supported the early research of Langmuir and his 
associates because of the obvious importance of their discoveries. 
Realizing that weather modification research was more properly a con- 
cern of the Federal Government, the company welcomed the interest 
of, and contract support from, the U.S. Army Signal Corps in 
February 1947. Subsequently, contract support was augmented by the 
Office of Naval Research, the U.S. Air Force provided flight support, 
and the U.S. Weather Bureau participated in a consultative role. The 
entire program which followed, through 1951, under this arrangement, 
including the field activities by Government agencies and the labora- 
tory work and general guidance by General Electric, was designated 
''Project Cirrus." 61 According to Byers : 

The most pronounced effect produced by Project Cirrus and subsequently sub- 
stantiated by a number of tests by others, was the clearing of paths through 
supercooled stratus cloud layers by means of seeding from an airplane with dry 
ice or with silver iodide. When such clouds were not too thick, the snow that was 
artificially nucleated swept all the visible particles out of the cloud. * * * In one 
of the first flights, * * * the supercooled particles in stratus clouds were removed 
using only 12 pounds of dry ice distributed along a 14-mile line. In later flights 
even more spectacular results were achieved, documented by good photography. BL ' 

Initial Project Cirrus studies were made during the summer of 
1947 on cumulus clouds near Schenectady, but the important seeding 
experiments were conducted the following year in New Mexico. Also 
during 1947, there was an attempt on October 13 to modify a hurricane 
east of Jacksonville, Fla., through seeding with dry ice. 63 Visual ob- 
servations, reported by flight personnel, seemed to indicate a pro- 
nounced change in the cloud deck after seeding, and, shortly there- 
after, the hurricane changed its course and headed directly westward, 
striking the coasts of Georgia and South Carolina. Even though there 
was precedent for such erratic behavior of hurricanes, there was 
speculation about the effect of seeding on the storm path, and the pos- 
sibility of legal responsibility for damages which might be caused by 

59 Lanfrmuir. Irvinp. "The Production of Rain by a Chain Reaction in Cumulus Clouds at 
Temperatures Above Freezing." Journal of Meteorology, vol. 5. No. 5. October 1948. p. 192. 
6°T?vprs. "Historv of Weather Modification." 1974. pp. 13-14. 

61 ThH.. p. 14. 

62 Thirl. 

M See discussion of Project Stormfury in ch. 5. p. 290 ff. 


such experiments in the future provided reason to avoid seeding 
thereafter any storms with the potential of reaching land. The legal 
counsel of the General Electric Co. admonished Langmuir not to 
relate the course of the hurricane to the seeding; however, throughout 
the remainder of his career he spoke of the great benefit to mankind of 
weather control and of the potential ability to abolish evil effects of 
hurricanes. As a result, it was expected that the U.S. Weather Bu- 
reau would undertake massive efforts in weather control. Meteorolo- 
gists within and without of the Bureau were in a defensive position, 
with many other scientists, impressed by Langmuirs arguments, op- 
posing their position. Thus great controversies which developed 
between Langmuir and the Weather Bureau and much of the meteoro- 
logical community followed these and other claims, and often 
resulted from the fact that Langmuir did not seem to fully comprehend 
the magnitude and the mechanisms of atmospheric phenomena. 04 

Langmuir wanted to ^work where he thought storms originated 
rather than in upstate New York. He chose Xew Mexico as operations 
area for Project Cirrus, also taking advantage of the opportunity to 
collaborate there with Dr. E. J. Workman at the New Mexico Institute 
of Mining and Technology, whose thunderstorm research included 
radar observations and laboratory experiments on the effects of ire 
on storm electrification. After cloud-seeding flights there in October 
1948, Langmuir reported that, as a result of the seeding, rainfall had 
been produced over an area greater than 40,000 square miles (about 
one-fourth the area of the State of New Mexico) . 63 

The Project Cirrus group returned to Xew Mexico in July 1040, 
and 10 additional seeding nights were conducted. When Langmuir 
learned that Vonnegut was dispensing silver iodide from a ground 
generator in the same area and had, in fact, also been doing so during 
the flights of the previous October, he concluded that both the July 
1919 results and the widespread effects of October 1948 were caused 
by the silver iodide rather than the dry ice seeding as he had theorized 
previously. Spectacular results continued to be reported by him. 
spurred on by meteorologists' challenges to his statistical methods 
and conclusions. Noting that Vonnegut had operated the ground 
generator only on certain days, Langmuir observed that rainfall 
responses corresponded to generator "on" times, leading him to his 
controversial "periodic seeding experiment.'' to which the remainder 
of his life was devoted. 66 

In the periodic seeding experiment, the silver iodide generators were 
operated in an attempt to effect a 7-day periodicity in the behavior of 
various weather properties. Langmuir was convinced that unusual 
weekly weather periodicities in early 1950 resulted from periodic seed- 
ings begun in Xew Mexico in December 1949. concluding that the effects 
were more widespread than he felt earlier and that temperatures and 
pressures thousands of miles away were also affected. Meteorologists 
observed that, while these correlations were the most striking seen, yet 
such periodicities were not uncommon. 67 The Weather Bureau under- 
took a study of records from 1919 to 1951 to see if such weather perio- 

" Ibid., pp. 14-16. 
■ Ibid., p. 1«. 
w Ibid., p in. 
r ~ Ibid., pp. in 20. 


dickies had occurred in the past. Glenn W. Brier, author of the report 
on this study, indicated that a T-day component in the harmonic anal- 
ysis of the data appeared frequently, though seldom as marked as dur- 
ing the periodic seeding experiment. 68 Byers' opinion is that the evi- 
dence appeared just as reliable for occurrence of a natural periodicity 
as for one controlled artificially. He contends that the most important 
discoveries in cloud physics and weather modification were made in the 
General Electric Research Laboratory before Project Cirrus was orga- 
nized, that the effect of clearing stratus decks was shown soon after the 
project was underway, and that the seeding experiments thereafter 
became more of a "program of advocacy than of objective proof." The 
project * * failed to demonstrate that seeding of cumulus clouds 
increased rainfall, that seeding initiates self -propagating storms, that 
the atmosphere responds periodically to periodic seeding, or that a 
hurricane could be deflected in its path by seeding." 69 

Seeding under Project Cirrus ended in 1951 and the final report 
appeared in 1953. After the close of the project, Langmuir continued 
his analyses and wrote two more papers before his death in 1957. The 
final paper was titled "Freedom — the Opportunity To Profit From the 
Unexpected." a report that Byers feels provided a fitting philosophical 
close to his career. 70 The Defense Department sponsored another series 
of experiments, called the Artificial Cloud Xucleation Project, from 
1051 to 1953. 

Tlie Weather Bureau Cloud Physics project 

Amid increasing publicity and spectacular claims of results from 
cloud seeding in Project Cirrus, the U.S. Weather Bureau initiated in 
1048 a project to test cloud seeding, with the cooperation of the Na- 
tional Advisory Committee for Aeronautics, the Navy, and the Air 
Force. The Cloud Phvsics Project, the first systematic series of seeding 
experiments in stratiform and cumuliform clouds, continued for 2 
years, with flight operations in Ohio, California, and the Gulf States. 
Findings of Project Cirrus were substantiated in that striking visual 
cloud modifications occurred: however, there was no evidence to show 
spectacular precipitation effects, and the experiments led to a conserva- 
tive assessment of the economic importance of seeding. 71 Cloud dissi- 
pation rather than new cloud development seemed to be the general 
result from seeding, the only precipitation extractable from clouds was 
that contained in the clouds themselves, and cloud seeding methods did 
not seem to be promising for the relief of drought. 72 

Bosults of the cloud physics experiment had almost no effect on 
the prevalent enthusiasm at the time for rainmaking through cloud 
soedino-, oxcent in the "hard core" of the meteorology community. 73 
As r result of thes<* experiments and the interpretation of the results, 
the TToather Bureau and its successor organizations in the Commerce 
Department, the Environmental Science Services Administration and 
the "National Oceanic and Atmospheric Administration, have been 

os Brier. Glenn W.. "Seven-Dar Periodicities in May 19.~2." Bulletin of the American 
Me^eorolosricPl Societr. vol. 35. No. 3. March 1954. pp. 118-121. 
p? B^ers. "History of Weather Modification." 1974. pp. 20-21. 
70 Ibid., p. 20.. 

" Flpfisrle. Robert G.. "Background and Present Status of Weather Modification." 196S. 
pp 0-10. 

■ 2 B-ers. "^'storv of Weather Modification." 1074. pp. 10-17. 
»» Ibid,, p. 17. 


regarded by some critics as unimaginative and overconservative on 
weather modification. 74 

The U.S. experiments of 1953-54 

In 1951 the Weather Bureau, the Army, the Navy, and the Air Force 
appointed an advisory group, chaired by Dr. Sverre Petterssen of 
the University of Chicago, under whose advice and guidance the 
following six weather modification projects were initiated : 75 

1. Seeding of extratropical cyclones, sponsored by the Office of 
Naval Research and conducted by Xew York University. 

2. Seeding of migratory cloud systems associated with fronts and 
cyclones, conducted by the Weather Bureau. 

3. Treatment of connective clouds, supported by the Air Force and 
conducted by the University of Chicago. 

4. Research on the~dissipation of cold stratus and fog, conducted 
by the Army Signal Corps. 

5. Studies of the physics of ice fogs, sponsored by the Air Force 
and conducted by the Stanford Research Institute. 

6. Investigation of a special warm stratus and fog treatment svs- 
tem, sponsored by the Army and conducted by Arthur D. Little, Inc. 

Field experiments on these projects were carried out in 1953 and 
1954, and reports were published under the auspices of the American 
Meteorological Society in 195T. 76 

The purpose of the extratropical cyclone seeding project, called 
Project Scud, was to "* * * ascertain whether or not it would be 
possible to modify the development and behavior of extratropical 
cyclones by artificial nucleation. * * *" 77 Analysis obtained in Scud 
from Florida to Long Island showed that "* * * the seeding in this 
experiment failed to produce any effects which were large enough to be 
detected against the background of natural meteorological variance." 7S 

The Weather Bureau project on migratory cloud systems was con- 
ducted in western Washington on cloud systems that enter the area 
from the Pacific during the rainy winter months. This project was 
criticized by commercial seeders since it was conducted in the West, 
which was considered "their territory," and by those who accused the 
Weather Bureau of seeking a negative result to support their conserva- 
tive view toward weather modification. Byers feels that there was an 
attempt to avoid this negative impression by giving a more positive 
interpretation to the results than the data possibly justified. 79 In sum- 
marizing results. Hall stated: 

Considering the results as a whole there is no strong evidence to support a con- 
clusion that the seeding produced measurable changes in rainfall. * * * the eval- 
uations do not necessarily furnish information on what the effect might have been 
with more or less intense seeding activity, rate of release of dry ice, etc. Also it 

71 Pleagle. "Background and Present Status of Weather Modification.'' 1998, p 10» 

« Byers, "History of Weather Modification," 1074. p. 25. 

7.) Prtterssen, Sverre. Jerome Sp;ir. Ferguson Hall. Roscoe R. Braham. Jr., Louis J. Rat- 
tan. Horace R. Byers, H. J. aufm Kamoe. J. J. Kelly, and H. K. Welcfcraann. "Cloud and 
Weather Modification; a Croup of Field Experiments." Meteorological Monographs, vol. 2. 
No 11 American Meteorological Society, Boston. 10."»7. Ill pp. 

"Petterssen, Sverre. "Reports on Experiments with Artificial Cloud Nucleation: Intro- 
ductory Note." In Petterssen et al . "Cloud and Weather Modification : ii Croup of Field 

Experiments," Meteorological Monographs, vol. 2. No. n. American Meteoroio.^icnl Society. 
Boston. 1957, p, S. 

T" Spar. Jerome "Prolecl Send." in Petterssen et al.. "Cloud mid Weather Modification ; 
:i Group of Field Experiments." Meteorological Monojrra plis. vol. 2. No. 11. American Mete- 
orological Society, P.oston. ior>7, n 22. 

"Byers. "History of Weather Modification," 1074. p. 26. 


might be speculated that the seeding increased rainfall on some occasions and 
decreased it on others. 80 

The aim of the University of Chicago Cloud Physics project was as 
follows : 81 

The formulation of a consistent and immediately applicable picture of the 
processes of formation of cumulus clouds, charged centers, and precipitation with 
a view toward testing the possibility that one can modify these processes and 
influence the natural behavior of clouds. 

So that as many cumulus clouds as possible could be tested, work was 
conducted in the Middle West in the summer and in the Caribbean in 
the winter, realizing that the warm trade-wind cumulus clouds in the 
latter region might be amenable to seeding with large hygroscopic 
nuclei or water spray, and that the ice-crystal process would operate to 
initiate precipitation in the colder clouds of the Middle West. 82, Of the 
numerous conclusions from this project 83 a few will serve to indicate 
the value of the project to the understanding of cloud phenomena and 
weather modification. In the Caribbean tests, water spray from an air- 
craft was seen to increase rainfall as determined by radar echoes ; anal- 
ysis showed that the treatment doubled the probability of occurrence of 
a radar echo in a cloud. From tests on dry ice seeding in the Middle 
West it was found that in the majority of cases treated clouds showed 
an echo, while untreated ones did not, although the sample was consid- 
ered too small to be significant. In all cases clouds were considered in 
pairs, one treated by seeding and the other untreated, and only those 
clouds showing no echo initially were chosen for study. 84 

The seeding experiments with supercooled stratus clouds by the 
Army Signal Corps essentially substantiated the results of Project 
Cirrus; however, from these carefully conducted tests a number of 
new relationships w^ere observed with regard to seeding rates, spread 
of glaciating effect, cloud thickness, overseeding, and cloud formation 
after seeding. S5 The report on this project carefully summarized these 
relationships and conclusions for both dry ice and silver iodide 
seeding. 86 

The Air Force project on the physics of ice fogs, conducted by 
Stanford Research Institute, was intended to learn the relationship 
to such fogs of synoptic situations, local sources of water, and pollu- 
tion. Investigations in Alaska at air bases showed that most fogs 
developed from local sources of water and pollution. In the Arthur L). 
Little investigation for the Army attempts were made to construct 
generators which were capable of producing space charges, associated 
with aerosols, that could bring about precipitation of the water drop- 
lets in warm fogs and stratus. 87 

» Hail, Ferguson. "The Weather Bureau ACN Project." In Petterssen et al., "Cloud and 
Weather Modification ; a Group of Field Experiments," Meteorological Monographs, vol. 2. 
No. 11. American Meteorological Society. Boston. 1957. pp. 45-46. 

sl Braham. Roscoe R., Jr.. Louis J. Battan. and Horace R. Byers. "Artificial Nucleation 
of Cumulus Clouds." In Petterssen et al.. "Cloud and Weather Modification : a Group of 
Field Experiments," 1957, p. 47. 

& Byers, "History of Weather Modification," 1974, pp. 26-27. 

83 Conclusions are precisely spelled out in somewhat technical terms in : Braham, Battan. 
and Byers. "Artificial Nucleation of Cumulus Clouds," 1957, pp. S2-S3. 
fi Byers, "History of Weather Modification," 1974, p. 27. 

86 IMd. . » , 

86 aufm Kampe, H. J., J. J. Kelly, and H. K. Weickmann, "Seeding Experiments m Sub- 
cooled Stratus Clouds." In Petterssen et al.. "Cloud and Weather Modification : a Group of 
Field Experiments." Meteorological Monographs, vol. 2, No. 11. American Meteorological 
Society. Boston, 1957, p. 93. , T . , . 

57 Petterssen, "Reports on Experiments With Artificial Cloud Nucleation: Introductory 
Note," 1957, p. 4. 


Brers, in retrospect, wonders why the results of this series of six 
experiments, which were carefully controlled statistically, did not 
receive more attention than was accorded them. He attributes some 
of this lack of visibility to the publication in the somewhat obscure 
monograph of the American Meteorological Society 88 and to the delay 
in publishing the results, since the Petterssen committee held the manu- 
scripts until all were completed, so that they could be submitted for 
publication together. 89 

Arizona mountain cumulus experiments 

After 1954, the University of Chicago group joined with the Insti- 
tute of Atmospheric Physics at the University of Arizona in seeding 
tests in the Santa Catalina Mountains in southern Arizona. These 
experiments were conducted in two phases, from 1957 through 1960 
and from 1901 through 1964, seeding mostly summer cumulus clouds, 
but some winter storms, with silver iodide from aircraft. In the first 
phase, analysis of precipitation data from the first 2 years revealed 
more rainfall during seeded than on nonseeded days ; however, during 
the latter 2 years, considerably more rainfall was achieved on non- 
seeded days. Combining all data for the 4 years of the first phase 
yielded overall results with more rain on unseeded days than on seeded 
days; hence, the experiments were modified and the second phase 
undertaken. Of the 3 years in the second phase, only one showed more 
rain on seeded days than on nonseeded ones. None of the analyses 
attempted could support the hypothesis that airborne silver iodide 
seeding increased precipitation or influenced its area! extent. Byers 
suggests that the failure to increase rainfall may have been due to the 
fact that precipitation initiation resulted from the coalescence process 
rather than the ice-crystal process. 90 

Project Whitetop 

According to Byers, perhaps the most extensive and most sophisti- 
cated weather modification experiment (at least up to the time of 
Byers' historical review in 1973) was a 5-year program of summer 
convective cloud seeding in south-central Missouri, called Project 
Whitetop. Conducted from 19G0 through 1964 by a group from the 
University of Chicago, led by Dr. Roscoe 11. Braham, the purpose of 
Whitetop was to settle with finality the question of whether or not 
summer convective clouds of the Midwest could be seeded with silver 
iodide to enhance or initiate precipitation. Experimental days were 
divided into seeding and no seeding days, chosen randomly from 
operational days suitable for seeding, based on certain moisture cri- 
teria. Another feature of the project was the attempt to determine the 
extent of spreading of silver iodide smoke plumes from the seeding 
line. Precipitation effects were evaluated by radar and by a rain-gage 
network. 01 

Final analysis of all of the Project Whitetop data showed that the 
overall effect was that, in the presence of silver iodide nuclei, the rain- 
fall was less than in the unseeded areas. Byers attributes these negative 

88 Petterssen et al.. "Cloud and Weather Modification; a Group of Field Experiments," 

*> livers. "History of Weather Modification," 11)74, p. 2S. 

»° Il)ld., p. 29. 

« Ibid., pp. 20-30. 


results to the physical data obtained from cloud-physics aircraft. "Most 
of the Missouri clouds produced raindrops by the coalescence process 
below the freezing line, and these drops were carried in the updrafts 
and frozen as ice pellets at surprisingly high subf reezing temperatures 
( — 5° C to —10° C)." He further points out that the measured con- 
centrations of ice particles, for the range of sizes present, were already 
in the natural unseeded conditions equivalent to those hoped for with 
seeding; consequently, the silver iodide only had the effect of over- 
seeding. 92 

Climax experiments 

Following the initial General Electric experiments, it was concluded 
by Bergeron 93 that the best possibility for causing considerable rain- 
fall increase by artifical means might be found in seeding orographic 94 
cloud systems. Consequently, there were almost immediate efforts to 
increase orographic precipitation, the greatest concentration of such 
work being in the Western United States. Commercial groups such 
as power companies and irrigation concerns took the early initiative in 
attempts to augment snowfall from orographic cloud systems in order 
to increase streamflow from the subsequent snowmelt. 

Colorado State University (CSU) began a randomized seeding 
experiment in the high Rocky Mountains of Colorado in 1960, under 
the direction of Lewis O. Grant, to investigate snow augmentation 
from orographic clouds. The project was designed specifically to 
(1) evaluate the potential, (2) define seedability criteria, and (3) de- 
velop a technology for seeding orographic clouds in central Colorado. 95 
It followed the 1957 report of the President's Advisory Committee for 
Weather Control, in which it had been concluded that seeding of oro- 
graphic clouds could increase precipitation by 10 to 15 percent, basing 
this judgment, however, on data from a large number of seeding pro- 
grams that had not been conducted on a random basis. 96 

The first group of the CSU seeding experiments took place from 
1960 to 1965 in the vicinity of Climax, Colo., and has been designated 
Climax I. A second set of tests in the same area from 1965 to 1970 
has been referred to as Climax II. The Climax experiments are impor- 
tant in the history of weather modification because they were the first 
intensive projects of their kind and also because positive results 
were reported. 97 The precipitation for all seeded cases was greater than 
for all of the unseeded cases by 9, 13, and 39 percent, respectively, for 
Climax I, Climax II, and Climax IIB. The latter set of data are a 
subsample of those from Climax II, from which possibly contaminated 
cases due to upwind seeding by other groups were eliminated. 98 

Ibid., p. 30. 

93 Bergeron, Tor, "The Problem of an Artificial Control of Rainfall on the Globe ; General 
Effects of Ice Nuclei in Clouds." Tellus, vol. 1, No. 1, February 1949, p. 42. 

94 A definition of orographic clouds, a discussion of their formation, and a summary of 
attempts to modify them are found in ch. 3, p. 71 ff. 

95 Grant, Lewis O., and Archie M. Kahan, "Weather Modification for Augmenting Oro- 
graphic Precipitation." In Wilmot N. Hess (editor), "Weather and Climate Modification," 
New York, Wiley, 1974, p. 295. 

98 Advisory Committee on Weather Control. Final Report of the Advisory Committee on 
Weather Control, Washington, D.C., U.S. Government Printing Office, Dec. 31, 1957, vol. I, 
p. vi. (The establishment of the Advisory Committee and its activities leading to publica- 
tion of its final report are discussed in ch. 5, under activities of the Congress and of the 
executive branch of the Federal Government, see pp. 195. 214, and 236.) 

97 Byers, "History of Weather Modification," 1974, pp. 30-31. „ 

98 Grant and Kahan, "Weather Modification for Augmenting Orographic Precipitation, 
1974, p. 298. 


Lightning suppression experiments 

From 1947 until the close of Project Cirrus, interspersed with his 
other activities, Vincent Schaefer visited U.S. Forest Service instal- 
lations in the northern Rockies in order to assist in attempts to sup- 
press lightning by cloud seeding. As early as 1949 an attempt was 
made to seed thunderstorm clouds with dry ice, dumping it from the 
open door of a twin-engine aircraft flying at 25,000 feet." This 
stimulated curiosity among those involved, but also showed that light- 
ning-prevention research w T ould require a long and carefully planned 
effort. These early activities led to the formal establishment of Proj- 
ect Skyfire in 1953, aimed at lightning suppression, as part of the 
overall research program of the Forest Service. Throughout the his- 
tory of the project, research benefited from the cooperation and sup- 
port of many agencies "and scientific groups, including the National 
Science Foundation, the Weather Bureau, Munitalp Foundation, the 
Advisory Committee on Weather Control, the National Park Service, 
General Electric Research Laboratories, Meteorology, Inc., and sev- 
eral universities. The project was phased out by the Forest Service 
in the 1970's, since results of years of tests were inconclusive, although 
there had been some reports of success. Skyfire was the longest con- 
tinuing Federal weather modification research project, enduring for 
about 20 years. 1 

Fog dispersal research 

Experiments were conducted on clearing supercooled fog from run- 
ways at Orly Airport in Paris since 1962, using sprays of liquid pro- 
pane. Soon after these successful tests, the method became operational 
and has already succeeded in various U.S. Air Force installations. The 
dissipation of cold fog is now operational also at many locations, 
including some in North America and in the Soviet Union. Warm fogs, 
however, are more common over the inhabited globe, and efforts to 
dissipate them had not advanced very far, even by 1970. 2 

Hurricane modification 

In an earlier discussion of the work of Langmuir and his associates 
under Project Cirrus, an attempt at hurricane modification was men- 
tioned. 3 The historical unfolding of hurricane research in the United 
States thereafter will not be reported here since it is discussed in detail 
in chapter 5, under Project Stormfury, now a major weather modifica- 
tion research program of the National Oceanic and Atmospheric Ad- 
ministration of the U.S. Department of Commerce. 4 

Hail suppression 

The principal lead in research to suppress hail during the 1950's and 
1960's was not in the United States, but mainly elsewhere, particularly 
in Switzerland, France, Italy, tho U.S.S.R., Argentina, Bulgaria, 
Yugoslavia, Kenya, and Canada. Hail suppression is based on the 

86 Barrows J S. "Preventing Fire from the Sky." In U.S. Department of Agriculture, 
"The Yearbook of Agriculture, 1968: Science for Better Living." Washington. D.C., U.S. 
Government Printing Office, 1968, p. 219. 

1 For a more detailed discussion of Project Skyfire, see p. 309, under the weather modi- 
fication program of the Department of Agriculture in ch. r>. 

2 Byers, "History of Weather Modification," 1974, p. 33. 

3 See p. 39. 

* See p. 296. 


hypothesis that, if a cloud is supplied with a superabundance of ice 
nuclei, the available water will be used to form a great number of snow 
crystals, thus depriving the hailstones of sufficient water to grow 
to damaging size. Most of the early foreign attempts to suppress hail 
using explosive rockets or ground-based silver iodide generators 
proved disappointing. 5 

In the Soviet Union, the Caucasus hail suppression experiments of 
the mid-1960's were of great interest to cloud physicists. Using radar 
to locate the zone of greatest water content in convective clouds and 
rockets with explosive warheads to deliver lead iodide with precision 
into this zone, the Russians claimed success in suppressing hailstorms, 
based on statistical reduction in crop damages. Operational hail sup- 
pression activity is now conducted on a large scale in the Soviet 
Union. 6 - 7 Most hail suppression efforts in the United States in the 
1960's were commercial operations which did not produce data of any 
significant value for further analysis. 

Foreign weather modification research 

While the Russians and some other countries have concentrated on 
hail suppression research, Australia, like the United States, has been 
principally concerned with augmenting precipitation. Very shortly 
after Schaefer first seeded a natural cloud with dry ice, Krauss and 
Squires of the Australian Weather Bureau seeded stratonimbus clouds 
in February 1947 near Sidney. The Commonwealth Scientific and 
Industrial Research Organization (CSIRO) subsequently organized, 
under Dr. E. G. Bowen, what might then have been the world's out- 
standing group of cloud physics and weather modification scientists. 
Byers feels that probably "* * * no other group contributed more to 
practical cloud physics during the period approximately from 1950 to 
1965." 8 

The Snowy Mountain project in Australia, whose object was to pro- 
duce a significant precipitation increase over the mountains by silver 
iodide seeding, has attracted most attention. For a 5-year period from 
1955 through 1959, this experiment was conducted during the colder 
part of the Southern Hemisphere year, using silver iodide dispensed 
from aircraft. Although initial experimental reports indicated suc- 
cessful increases in precipitation over the target, the final 1963 re- 
port after complete analysis stated that results were encouraging but 
inconclusive. 9 

Interesting experiments were carried out in Israel during the 1960's, 
using airborne silver iodide seeding of mostly cumulus clouds. Statis- 
tical analysis of data from the first 5% years of tests revealed an in- 
crease of 18 percent in rainfall. 10 

A project called Gross versuch III was conducted on the southern 
slopes of the Alps in Switzerland. Although initiated as a randomized 
hail suppression experiment, using ground-based silver iodide gen- 
erators, the analysis indicated that hail frequency was greater on 

5 Byers, "Histry of Weather Modification," pp. 31-32. 

6 Ibid., p. 32. 

7 The hail suppression efforts of the U.S.S.R. are discussed in more detail under the status 
of hail suppression technology in ch. 3, p. 88, and under foreign programs in ch. 9, 412. 

8 Byers, "History of Weather Modification," 1974, p. 23. 

9 Ibid., pp. 23-24. 
" Ibid., p. 31. 


seeded than on nonseeded days, but that the average rainfall on seeded 
days was 21 percent greater than on nonseeded days. 11 


In the weeks and months following Schaefer's first cloud seeding 
experiment public interest grew, and Langmuir and Schaefer spoke 
before and consulted with groups of water users, farmers and ranchers, 
city officials, Federal program directors, and scientific societies. As a 
result there was a burgeoning of new cloud-seeding efforts initiated by 
commercial operators, industrial organizations, water districts, and 
groups of farmers. Some used ground generators for dispensing silver 
iodide obviating the need for airplanes and their attendant high costs, 
so that many such opepations became quite profitable. Many rain- 
makers were incompetent and some were unscrupulous, but their activi- 
ties flourished for a while, as the experiments of Shaefer and Lang- 
muir were poorly imitated. Some of the more reliable companies are 
still in business today, and their operations have provided data valu- 
able to the development of weather modification technology. 12 

Byers relates a few instances of early commercial operations of 
particular interest. 13 In 1949-50 the city of New York hired Dr. Wal- 
lace E. Howell, a former associate of Langmuir, to augment its water 
supply by cloud seeding. New York's citizenry became interested and 
involved in discussions over Howell's activities as the news media made 
them known. This project was also the first case where legal action was 
taken against cloud seeding by persons whose businesses could be 
adversely affected by the increased rain. Although rains did come and 
the city reservoirs were filled, Howell could not prove that he was re- 
sponsible for ending the drought. 14 Howell subsequently seeded in 
Quebec in August 1953 in an attempt to put out a forest fire and in 
Cuba to increase rainfall for a sugar plantation owner. 15 

The Santa Barbara project in California, also a commercial opera- 
tion designed to increase water supply, received a great deal of atten- 
tion. In this period water was increased through augmenting rain and 
snow in the mountains north and northeast of the city. The project 
was evaluated by the California State Water Resources Board and 
was unique among commercial contract operations, inasmuch as the 
clients permitted randomization (that is, random selection of only 
some storms for seeding) in order to allow adequate evaluation. 16 

In the West the earliest commercial operations were developed 
under Dr. Irving P. Krick, formerly head of the Department of Mete- 
orology at the California Institute of Technology. Asked to monitor 
aerial dry ice seeding over Mt. San Jacinto in 1947, Krick became 
interested in weather modification, left Caltech, and formed his own 
company. Seeding projects were carried out during 1948 and 1949 for 
ranchers in San Diego County, Calif., in Mexico, and in Arizona. In 
1050 lie moved to Denver and formed a new company, which began 
seeding activity over the Great Plains, elsewhere in the West, and in 

" Ibid. 

12 Ibid., pp. 17, 21. 22. 
" Ibid., pp. 22-23. 
w Ibid., p. 22. 

15 Hnlacv. "The Weather Chancers, " 1968, pp. 96-97. 
"Ibid., pp. 22-23. 


other countries. A number of former students of Krick joined him or 
formed other cloud seeding companies, mostly in the West during the 
1950's. 17 By 1953 Krick had operated 150 projects in 18 States and 6 
foreign countries and amassed over 200,000 hours of seeding time. For 
three winters — 1949, 1950, and 1951 — his company claimed that they 
had increased the snowpack in the Rockies around Denver from 175 to 
288 percent over the average of the previous 10 years. After 6 months 
of seeding in Texas in 1953, the water in a drainage basin near Dallas 
had increased to 363 percent of the January 1 level, while in nearby 
nonseeded basins water ranged from a 22-percent deficit to an increase 
of 19 percent. 18 

At the start of extensive seeding in the early 1950's there was a sharp 
increase in commercial operations, accompanied by great publicity as 
drought began in the Great Plains. During the middle and latter 1950's, 
however, seeding diminished as did the drought. The some 30 annual 
seeding projects in the United States during the mid and latter 1950's 
and the 1960's (excluding fog clearing projects) were conducted for 
the most part by about five firms, on whose staffs there were skilled 
meteorologists, cloud physicists, and engineers for installing and main- 
taining ground and air systems. Most of these projects were in the 
categories of enhancing rain or snowfall, with a distribution in a 
typical year as follows : About a dozen in the west coast States, half 
a dozen in the Rocky Mountains-Great Basin area, half a dozen in 
the Great Plains, and the remainder in the rest of the United States. 
Of the projects in the West, six to nine have been watershed projects 
sponsored by utility companies. Most of these projects endured for 
long periods of years and many are still underway. 19 

Fleagle notes that by the early 1950's, 10 percent of the land area 
of the United States was under commercial seeding operations and 
$3 million to $5 million was being expended annually by ranchers, 
towns, orchardists, public utilities, and resort operators. The extent 
of such commercial operations receded sharply, and by the late 1950's 
business was only about one-tenth or less than it had been a decade 
earlier. As noted above, public utilities were among those who con- 
tinued to sponsor projects throughout this period. 20 

Figure 1 shows the purposes of weather modification operations for 
various sections of the United States for the period July 1950 through 
June 1956. For each geographical section the column graphs represent 
the percentage of the total U.S. seeding for each of five purposes that 
was performed in that section. The bar graph in the inset shows the 
percentage of total U.S. cloud-seeding effort that is undertaken for 
each of these five purposes. Figure 2 shows the total area coverage 
and the percent of U.S. territory covered by cloud seeding for each 
year from July 1950 through June 1956. Both figures are from the 
final report of the President's Advisory Committee on Weather 
Control. 21 

17 Elliott, Robert D., "Experience of the Private Sector," 1974, p. 47. 

18 Halacy, "The Weather Changers," 1968, p. 96. 

19 Elliott, "Experience of the Private Sector," 1974, p. 46-48. 

20 Fleagle, "Background and Present Status of Weather Modification." 1968, p. 11. 

21 Advisory Committee on Weather Control, Final Report, 1958, vol. II. Figures lacing 
p. 242 and 243. 

Figure 1 — Purposes of weather modification operations conducted in various 
geographical sections of the United States, July 1950 through June 1956. (From 
Final Report of the Advisory Committee on Weather Control, 1958.) 




1950- 1951- 1952- 1953- (954- 1935- 

1951 1952 1953 1954 1955 1936 

Figure 2. — Total area coverage and percent of area coverage for the 48 cotermi- 
' nous States of the United States by weather modification operations for each 

year, July 1950 through June 1956. (From Final Report of the Advisory 

Committee on Weather Control, 1958.) 

Table 1 is a summary of weather modification operations for fiscal 
years 1966, 1967, and 1968, compiled by the National Science Founda- 
tion from field operators' reports which the Foundation required to be 
filed. Figure 3 shows the locations in the continental United States for 
both operational and research weather modification projects during 
fiscal year 1968. In September 1968, as provided by Public Law 90-407, 
the National Science Foundation was no longer authorized to require 
the submission of reports on operational weather modification proj- 
ects. 22 Weather modification activities are now reported to the Depart- 
ment of Commerce, under provisions of Public Law 92-205, and sum- 
mary reports of these activities are published from time to time. 23 

22 See discussions of this law and of the activities of the National Science Foundation as 
lead weather modification acency through September 1968. pp 196 and 215 in ch. 5. 

23 See discussions of Public Law 92-205 and of the weather modification activities report- 
ing program in ch. 5, 197 and 232. The activities summarized in the latest available 
Department of Commerce report are discussed in ch. 7 and listed in app. G. 



Area treated Number of Number of Number of 

(square miles) projects States 2 operators 2 

Purpose 1966 1967 1968 1966 1967 1968 1966 1967 1968 1966 1967 1968 

Rain augmentation and snow- 
pack increase 61,429 62,021 53,369 35 41 37 21 20 21 22 25 23 

Hail suppression 20,566 20,556 13,510 3 4 4 3 3 5 3 4 4 

Fog dissipation 100 118 145 22 15 15 15 13 9 17 15 10 

Cloud modification 19,345 28,300 18,600 9 18 8 8 12 7 8 14 6 

Lightning suppression 314 314 314 1 1 1 1 1 1 1 1 1 

Totals... 101,744 111,383 85,938 70 79 65 30 23 25 46 44 37 

1 Data for fiscal year 1968 include reports received to Sept. 1, 1968. 

2 Totals are not the sum of the items since many States and operators are involved in more than one type of activity. 

An early commercial hail suppression project was begun in Colorado 
in 1958. Eventually it involved 5 seeding aircraft and about 125 
ground-based generators "making it the largest single cloud-seeding 
project up to that time. Results of the project were examined at Colo- 
rado State University and presented at the International Hail Con- 
ference in Verona, Italy, in 1960. This project stimulated the interest 
of scientists and provided historical roots for what later was estab- 
lished as the National Hail Research Experiment in the same area over 
a decade later by the National Science Foundation. 2 ' 4 ' 25 

During the 1960's, clearing of cold airport fog through cloud seed- 
ing became an operational procedure. Since the techniques used can 
only be applied to cold fog, they were used at the more northerly 
or high-altitude airports of the United States, where about 15 such 
projects were conducted, and are still underway, each winter. 2,6 

2 * Elliott, "Experience of the Private Sector," 1974, p. 48. 

23 The National Hail Research Experiment is discussed in detail under the weather modi- 
fier lion program ol" the Xationa' Science Foundation in ch. 5 ; se p. 274ff. 
28 Elliott, "Experience of the Private Sector," 1974. pp. 48-49. 


Figure 3. — Weather modification projects in the United States during fiscal year 
1968. (From NSF Tenth Annual Report on weather modification, 1968.) 



In the various discussions under activities of the Congress and the 
executive branch of the Federal Government in chapter 5, there are 
historical accounts of legislative actions pertinent to weather modifica- 
tion, of the establishment and functioning of special committees in 
accordance with public laws or as directed by the executive agencies, 
and of the policy and planning studies and reports produced by the 
special committees or by the agencies. Inclusion of a separate historical 
account of these Federal activities at this point would be largely repeti- 
tive, and the reader is referred to the various sections of chapter 5, in 
which historical developments of various Federal activities are un- 
folded as part of the discussions of those activities. 




(By Robert E. Morrison, Specialist in Earth Sciences, Science Policy Research 
Division, Congressional Research Service) 


Although the theoretical basis for weather modification was laid to 
a large extent during the 1930's, the laboratory and field experiments 
which ushered in the "modern era" occurred in 1946 and in the years 
immediately thereafter. By 1950, commercial cloud seeding had become 
widespread, covering an estimated total U.S. land area of about 10 per- 
cent. 1 By the mid-1950's, however, it was apparent that the funda- 
mental atmospheric processes which come into play in weather 
modification are very complex and were far from being understood. A 
period of retrenchment and reevaluation began, the number of com- 
mercial operators had decreased dramatically, and weather modifica- 
tion had fallen into some disrepute among many meteorologists and 
much of the public. A period of carefully designed experiments was 
initiated about two decades ago, supported by increased cloud physics 
research and increasingly more sophisticated mathematical models and 
statistical evaluation schemes. 

Meanwhile, a small group of commercial operators, generally more 
reliable and more responsible than the typical cloud seeder of the 1950 
era, has continued to provide operational weather modification services 
to both public and private sponsors. These operators have attempted to 
integrate useful research results into their techniques and have pro- 
vided a bank of operational data useful to the research community. 
The operational and research projects have continued over the past two 
decades, often in a spirit of cooperation, not always characteristic of 
the attitudes of scientists and private operators in earlier years. Often 
the commercial cloud seeders have contracted for important roles in 
major field experiments, where their unique experiences have been 
valuable assets. 

Through the operational experiences and research activities of the 
past 30 years, a kind of weather modification technology has been 
emerging. Actually, though some practices are based on common theory 
and constitute the basic techniques for meeting a number of seeding 
objectives, there are really a series of weather modification technol- 
ogies, each tailored to altering a particular atmospheric phenomenon 
and each having reached a different state of development and opera- 
tional usefulness. At one end of this spectrum is cold fog clearing, con- 
sidered to be operational now, while the abatement of severe storms, at 

1 Fleagle. Robert G., "Background and Present Status of Weather Modification." In 
"Weather Modification : Science and Public Policy," Seattle, University of Washington 
Press, 1968, p. 11. 



the other extreme, remains in the initial research phase. Progress to 
date in development of these technologies has not been nearly so much 
a function of research effort expended as it has depended on the funda- 
mental atmospheric processes and the ease by which they can be altered. 
There is obvious need for further research and development to refine 
techniques in those areas where there has been some success and to 
advance technology were progress has been slow or at a virtual 


Recently, the following summary of the current status of weather 
modification technology was prepared by the Weather Modification 
Advisory Board : 

1. The only routine operational projects are for clearing cold fog. 
Research on warm fog has yielded some useful knowledge and good 
models, but the resulting technologies are so costly that they are usable 
mainly for military purposes and very busy airports. 

2. Several long-running efforts to increase winter snowpack by 
seeding clouds in the mountains suggest that precipitation can be 
increased by some 15 percent over what would have happened 

3. A decade and a half of experience with seeding winter clouds on 
the U.S. west coast and in Israel, and summer clouds in Florida, also 
suggest a 10- to 15-percent increase over "natural'' rainfall. Hypotheses 
and techniques from the work in one area are not directly transferable 
to other areas, but will be helpful in designing comparable experiments 
with broadly similar cloud systems. 

4. Xumerous efforts to increase rain by seeding summer clouds in the 
central and western parts of the United States have left many ques- 
tions unanswered. A major experiment to try to answer them — for the 
High Plains area — is now in its early stages. 

5. It is scientifically possible to open holes in wintertime cloud layers 
by seeding them. Increasing sunshine and decreasing energy con- 
sumption may be especially relevant to the northeastern quadrant of 
the United States. 

6. Some $10 million is spent by private and local public sponsors for 
cloud-seeding efforts, but these projects are not designed as scientific 
experiments and it is difficult to say for sure that operational cloud 
seeding causes the claimed results. 

7. Knowledge about hurricanes is improving with good models of 
their behavior. But the experience in modifying that behavior is primi- 
tive so far. It is inherently difficult to find enough test cases, especially 
since experimentation on tvphoons in the "Western Pacific has been 
blocked for the time being by international political objections. 

8. Although the Soviets and some U.S. private oi>erators claim some 
success in suppressing hail by seeding clouds, our understanding of the 
physical processes that create hail is still weak. The one major U.S. 
field experiment increased our understanding of severe storms, but 
otherwise proved mostlv the dimensions of what we do not vet know. 

0. There have been many efforts to suppress lightning by seeding 
thunderstorms. Our knowledge of the processes involved is fair, but 


the technology is still far from demonstrated, and the U.S. Forest 
Service has recently abandoned further lightning experiments. 2 

Lewis O. Grant recently summarized the state of general disagree- 
ment on the status of weather modification technology and its readiness 
for application. 

There is a wide diversity of opinion on weather modification. Some believe 
that weather modification is now ready for widespread application. In strong 
contrast, others hold that application of the technology may never be possible 
or practical on any substantial scale. 3 

He concludes that — 

Important and steady advances have been made in developing technology for 
applied weather modification, but complexity of the problems and lack of ade- 
quate research resources and commitment retard progress. 4 

In 1975, David Atlas, then president of the American Meteorologi- 
cal Society, expressed the following pessimistic opinion on the status 
of weather modification technology : 

Almost no one doubts the economic and social importance of rainfall augmenta- 
tion, hail suppression, fog dissipation, and severe storm abatement. But great 
controversy continues about just what beneficial modification effects have been 
demonstrated or are possible. Claims and counterclaims abound. After three 
decades of intense research and operational weather modification activities, only 
a handful of experiments have demonstrated beneficial effects to the general 
satisfaction of the scientific community. 

To describe weather modification as a "technology" is to encourage misunder- 
standing of the state of the weather modification art. The word "technology" 
implies that the major substantive scientific foundations of the field have been 
established and. therefore, that all that is required is to develop and apply tech- 
niques. But one of the conclusions of the special AMS study on cloud physics was 
that "the major bottleneck impeding developments of useful deliberate weather 
modification techniques is the lack of an adequate scientific base." 5 

At a 1975 workshop on the present and future role of weather modi- 
fication in agriculture, a panel of 10 meteorologists assessed the ca- 
pabilities for modifying various weather and weather-related phenom- 
ena, both for the present and for the period 10 to 20 years in the fu- 
ture. Conclusions from this assessment are summarized in table 1. The 
table shows estimated capabilities for both enhancement and dissipa- 
tion, and includes percentages of change and areas affected, where 
appropriate. 6 

A recent study by Barbara Farhar and Jack Clark surveyed the 
opinions of 551 scientists, all involved in some aspect of weather modi- 
fication, on the current status of various weather modification technol- 

2 Weather Modification Advisory Board. "A U.S. Policy to Enhance the Atmospheric 
Environment." Oct. 21, 1977. In testimony by Harlan Cleveland "Weather Modification." 
he-ring before the Subcommittee on the Environment arid the Atmosphere. Comnrtee on 
Science and Technology. U.S. House of Representatives. 95th Cong.. 1st sess.. Oct. 26, 1977. 
Washington. DC U.S. Government Prfnt'nsr Office. 1077. pp. 28-30. 

3 Grant. Lewis 0., "Scientific and Other Uncertainties of Weather Modification." In Wil- 
liam A. Thomas (editor). "Legal and Scientific Uncertainties of Weather Modification.' 
Proceedings of a symposium convened at Duke University, Mar. 11-12. 1976, by the 
National Conference of Lawyers and Scientists. Durham. N.C., Duke University Press. 
1977. p. 7. . 

4 Ibid., p. 17. 

5 Atlas. David. "Selling Atmospheric Science. The President's Page." Bulletin of the 
American Meteorological Societv. vol. 56. No. 7. July 1975. p. 6SS. 

6 Grant. Lewis O. and John D. Reid (compilers). "Workshop for an Assessment of the 
Present and Potential Role of Weather Modification in Agricultural Production." Colorado 
State Universitv. Fort Collins. Colo., July 15-1S. 1975. August 1975. PB-245-633. pp. 


ogies. 7 Table 2 is a summary of the assessments of the level of develop- 
ment for each of 12 such technologies included in the questionaire to 
which the scientists responded, and table 3 shows the estimates of ef- 
fectiveness for 7 technologies where such estimates are pertinent. Re- 
sults of this study were stratified in accordance with respondents' af- 
filiation, specific education, level of education, age, and responsibility 
or interest in weather modification, and tabulated summaries of 
opinions on weather modification in accordance with these variables ap- 
pear in the report by Farhar and Clark. 8 


[From Grant and Reid, 1975) 

Enhancement Dissipation 

Amount Amount 

change Area change Area 

(per- (square (per- (square 

Modified variable Now 10 to 20 yr cent) miles) Now 10 to 20 yr cent) miles) 

I. Clouds: 

1. Cold stratus No (8) 

2. Warm stratus No (10) 

3. Fog, cold Yes (10) 

4. Fog, warm Yes (10) 

5. Fog, artifical (for 

temperature con- 
trol) Yes (10) 

6. Contrails Yes (10) 

7. Cirrus... Yes (5) 

8. Carbon black No (10) 

9. Aerosol Yes (7) 

II. Convective precipitation: 

1. Isolated small Yes (7) 

2. Isolated large No (6) 

3. Squall lines Yes (5) 

4. Nocturnal Yes (5) 

5. Imbedded cyclonic. . Yes (9) 

6. Imbedded Oro- 

graphic Yes (9) 

III. Stratoform precip- 

1. Orographic Yes (10) 

2. Cyclonic No (10) 

3. Cloud water collec- 

tion Yes (10) 

IV. Hazards: 

1. Hail Yes (5) 

2. Lightning Yes (7) 

3. Erosion— wind 

gradient No (10) 

4. Erosion— water 

drop size Yes (5) 

5. Wind— hurricane No (5) 

6. Tornado. No (10) 

7. Blowdown No (5) 

8. Floods— symoptic ... No (10) 

9. Floods— mesoscale... No (9) 

10. Drought No (10) 

V. Other: 

1. Albedo Yes (5) 

2. Surface roughness... No (6) 

3. Topography changes. No (6) 

Yes (7) 1-1000 

No (5) 

Yes (10) 1-10 

Yes (10) 1-100 

Yes (10) 1-10 

Yes (10) 100-1000 

Yes (10) 100-1000 

No (6) 

Yes (10) 

Yes (10) 100 10-100 
Yes (7) 15 100-1000 
Yes(S) 20 100-10,000 
Yes (6) 100 100-1000 
Yes (10) 30 300-6000 

Yes (10) 20 300-6000 

Yes (10) Yes (10) 1-1000 

No (8) Yes (9) 

Yes (10) Yes (10) 1-1000 

Yes (10) Yes (10) 1-1 

N/A N/A 

No (10) No (10) 

No (10) No (8) 

N/A N/A 

N/A N/A 

Yes (5) Yes (8) 100 10-100 

Yes (5) Yes (8) 15 10-1000 

No (8) Yes (5) 20 100-10,000 

No (8) Yes (5) 100 100-1000 

Yes (8) Yes (10) <5 300-6000 

Yes (8) Yes (10) 20 300-6000 

Yes (10) 10 100-3000 Yes (10) Yes (10) 10 100-3000 
No (6) No (10) No (6) 

Yes (10) .... 

Yes (7) (i) 

Yes (9) (■) 

No(10) .... 


100-60,000 Yes 
40,000 Yes (7) 


Yes (9) 


No (10) No (10) 

Yes (7) 0) 10,000 Yes (5) 

Yes (6) No (6) 

Yes (5) No (10) 

Yes (5) No (9) 

No (10) No (10) 

Yes (6) No (9) 

No (10) Yes (5) 

Yes (7) 10,000 

Yes (6) 

Yes (5) 

Yes (5) 

No (3) 

Yes (6) 

Yes (6) 

Yes (10) 
Yes (6) 
Yes (5) 

Yes (5) 
No (6) 
No (6) 

Yes (10) 

Yes (6) 

Yes (5) 10-100 

1 Uncertain. 

7 Farhar. Barbnra C. and Jack A. Clark. "Can Wp Modify the Weather? a Survey of 
Scientists " Final report, vol. 3 (draft), Institute of Behavioral Science. University of Colo- 
rado. Boulder, Colo.. January 1078. (Based on research supported by the National Science 
Foundation under grants No*. ENV74-1R013 AOS. 01-35452, GI-44087. and BRT74-18613, 
as part of "A Comparative Analysis of Public Support of and Resistance to Weather Modi- 
fication Projects.") 89 pp. 

* Ibid. 



[From Farhar and Clark, 1978] 

Operations 1 Research 2 Neither Don't know Other 







Weather modification technology 












Cold fog dispersal 









Precipitation enhancement, winter oro- 



1 1 
1 1 




Precipitation enhancement, winter oro- 

graphic, maritime 










Hail suppression 










Precipitation enhancement, summer convec- 

tive, continental . 










Precipitation enhancement, summer convec- 

tive, maritime 










Warm fog dispersal... 









Precipitation enhancement with hail sup- 












Precipitation enhancement, general storms.. 











Lightning suppression 










Hurricane suppression 











Severe storm mitigation 











1 This category is a combination of two responses: "The technology is ready for operational application" and "The 
technology can be effectively applied; research should continue." 

2 This category is a combination of two responses: "The technology is ready for field research only" and "The technology 
should remain at the level of laboratory research." 




In a previous review of weather modification for the Congress, three 
possible classifications of activities were identified — these classifica- 
tions were in accordance with (1) the nature of the atmospheric proc- 
esses to be modified, (2) the agent or mechanism used to trigger or 
bring about the modification, or (3) the scale or dimensions of the 
region in which the modification is attempted. 9 The third classifica- 
tion was chosen in that study, where the three scales considered were 
the microscale (horizontal distances, generally less than 15 kilometers) , 
the mesoscale (horizontal distances generally between 15 and 200 
kilometers), and the macroscale (horizontal distances generally 
greater than 200 kilometers). 10 Examples of modification of processes 
on each of these three scales are listed in table 4, data in which are 
from Hartman. 11 Activities listed in the table are illustrative only, 
and there is no intent to indicate that these technologies have been 
developed, or even attempted in the case of the listed macroscale 


[Information from Hartman, 19661 
Scale Horizontal dimensions Examples of modification processes 

Microscale Less than 15 km 

Mesoscale 15 to 200 km. 

Macroscale Greater than 200 km. 

Modification of human microclimates. 
Modification of plant microclimates. 
Evaporation suppression. 
Fog dissipation. 
Cloud dissipation. 
Hail prevention. 

Precipitation through individual cloud modification. 

Precipitation from cloud systems. 

Hurricane modification. 

Modification of tornado systems. 

Changes to global atmospheric circulation patterns. 

Melting the Arctic icecap. 

Diverting ocean currents. 

In this chapter the characteristics and status of weather modifica- 
tion activities will be classified and discussed according to the nature 
of the processes to be modified. This seems appropriate since such a 
breakdown is more consonant with the manner the subject has been 
popularly discussed and debated, and it is consistent with the direc- 
tions in which various operational and research activities have moved. 
Classification by the second criterion above, that is, by triggering 
agent or mechanism, focuses on technical details of weather modi- 
fication, not of chief interest to the public or the policymaker, although 
these details will be noted from time to time in connection with dis- 
cussion of the various weather modification activities. 

In the following major section, then, discussion of the principles 
and the status of planned weather modification will be divided accord- 

9 Hartman. Lawton M.. "Characteristics and Scope of Weather Modification. In U.S. 
Congress, Senate Committee on Commerce. "Weather Modification and Control," TV ashing- 
ton. D.C., U.S. Government Printing Office. 1966. (89th Cone:.. 2d sess., Senate Kept. JSo. 
1139. prepared by the Legislative Reference Service, Library of Congress), p. 20. 

10 Ibid. 

" Ibid., pp. 21-31. 

34-857 O - 79 - 7 


ing to the major broad categories of phenomena to be modified; these 
will include : 

Precipitation augmentation. 

Hail suppression. 

Fog dissipation. 

Lightning suppression. 

Severe storm mitigation. 
In subsequent major sections of this chapter there are reviews of 
some of the specific technical problem areas common to most weather 
modification activities and a summary of recommenced research 

In addition to the intentional changes to atmospheric phenomena 
discussed in this chapter, it is clear that weather and climate have also 
been modified inadvertently as the result of man's activities and that 
modification can also be brought about through a number of natur- 
ally occurring processes. These unintentional aspects of weather and 
climate modification will be addressed in the following chapter of 
this report. 12 

Principles and Status of Weather Modification Technologies 

Before discussing the status and technologies for modification of 
precipitation, hail, fog, lightning, and hurricanes, it may be useful to 
consider briefly the basic concepts of cloud modification. The two major 
principles involved are (1) colloidal instability and (2) dynamic ef- 
fects. Stanley Changnon describes how each of these principles can 
be effective in bringing about desired changes to the atmosphere : 13 

Altering colloidal stability. — The physical basis for most weather modification 
operations has been the belief that seeding with certain elements would produce 
colloidal instability in clouds, either prematurely, to a greater degree, or with 
greater efficiency than in nature. Most cloud seeding presumes that at least a por- 
tion of the treated cloud is supercooled, that nature is not producing any or 
enough ice at that temperature of the cloud, and that treatment with chemical 
agents of refrigerants will change a proportion of the cloud to ice. The resultant 
mixture of water and ice is unstable and there is a rapid deposition of water 
vapor upon the ice and a simultaneous evaporation of water from the super- 
cooled droplets in the cold part of the cloud. The ice crystals so formed become 
sufficiently large to fall relative to remaining droplets, and growth by collection 
enhances the probability that particles of ice or water will grow to be large 
enough to fall from the cloud and become precipitation. 

This process of precipitation enhancement using ice nucleants has been dem- 
onstrated for the stratiform type cloud, and generally for those which are oro- 
graphically-produced and supercooled. Cumulus clouds in a few regions of the 
United States have also been examined for the potential of colloidal instability in 
their supercooled portions. This has been founded on beliefs that precipitation 
(1) can be initiated earlier than by natural causes, or (2) can be produced from 
a cloud which was too small to produce precipitation naturally. 

Seeding in the warm portion of the cloud, or in "warm clouds" (below the 
freezing level), has also been attempted so as to alter their colloidal instability. 
Warm-cloud seeding has primarily attempted to provide the large droplets neces- 
sary to initiate the coalescence mechanism, and is of value in clouds where insuffi- 
cient large drops exist. In general alteration of the coalescence process primarily 
precipitates out the liquid water naturally present in a cloud, whereas the ice- 
crystal seeding process also causes a release of latent energy that conceivably 
results in an intensification of the storm, greater cloud growth, and additional 

Alirrhifj cloud dynamics. — The effects to alter the colloidal instability of 
clouds, or their microphysical processes, have been based on the concept of rain 

1L ' Sof p. 145. 

13 Chnncrnon. Stanley A.. Jr. "Prosont and Future of Woathor Modification ; Peprtonal 
Issues." The Journal of Woathor Mortification, vol. 7. No. 1, April 1075, pp. 154-156. 


increase through increasing the precipitation efficiency of the cloud. Simpson 
and Dennis (1972) showed that alterations of cloud size and duration by "dynam- 
ic modification" could produce much more total rainfall than just altering the 
precipitation efficiency of the single cloud. In relation to cumulus clouds, 
"dynamic seeding" simply represents alteration one step beyond that sought 
in the principle of changing the colloidal stability. In most dynamic seeding 
efforts, the same agents are introduced into the storm but often with a greater 
concentration, and in the conversion of w r ater to ice, enormous amounts of 
latent heat are hopefully released producing a more vigorous cloud which will 
attain a greater height with accompanying stronger updrafts, a longer life, and 
more precipitation. Seeding to produce dynamic effects in cloud growth, whether 
stratiform or cumuliform types, is relatively recent at least in its serious in- 
vestigation, but it may become the most important technique. If through con- 
trolled cloud seeding additional uplift can be produced, the productivity in terms 
of rainfall will be higher whether the actual precipitation mechanism involved 
is natural or artificial. 

It has been proposed that the selective seeding of cumulus clouds also can 
either (a) bring upon a merger of tw T o or more adjacent clouds and a much 
greater rainfall production through a longer-lived, larger cloud * * * or (b) pro- 
duce eventually an organized line of clouds (through selective seeding of ran- 
domized cumulus). The latter could allegedly be accomplished by minimizing and 
organizing the energy into a few vigorous systems rather than a larger number of 
isolated clouds. 

Essentially, then, dynamic seeding is a label addressed to processes involved 
in altering cloud microphysics in a selective and preferential way to bring 
upon more rainfall through an alteration of the dynamical properties of the 
cloud system leading to the development of stronger clouds and mesoscale 
systems. Actually, dynamic effects might be produced in other ways such as 
alterations of the surface characteristics to release heat, by the insertion of 
chemical materials into dry layers of the atmosphere to form clouds, or by re- 
distribution of precipitation through microphysical interactions in cloud processes. 

The various seeding materials that have been used for cloud modi- 
fication are intended, at least initially, to change the microphysical 
cloud structure. Minute amounts of these materials are used with the 
hope that selected concentrations delivered to specific portions of the 
cloud will trigger the desired modifications, through a series of rapid 
multiplicative reactions. Seeding materials most often used are classi- 
fied as (1) ice nuclei, intended to enhance nucleation in the super- 
cooled part of the cloud, or (2) hygroscopic materials, designed to 
alter the coalescence process. 14 

Glaciation of the supercooled portions of clouds has been induced 
by seeding with various materials. Dry ice injected into the subfreezing 
part of a cloud or of a supercooled fog produces enormous numbers of 
ice crystals. Artificial ice nuclei, with a crystal structure closely re- 
sembling that of ice, usually silver iodide smoke particles, can also 
produce glaciation in clouds and supercooled fogs. The organic fer- 
tilizer, urea, can also induce artificial glaciation, even at temperatures 
slightly warmer than freezing. Urea might also enhance coalescence in 
warm clouds and warm fogs. Water spray and fine particles of sodium 
chloride have also been used in hygroscopic seeding, intended to alter 
the coalescence process. There have been attempts to produce co- 
alescence in clouds or fog using artificial electrification, either with 
chemicals that increase droplet combination by electrical forces, or 
with surface arrays of charged wires whose discharges produce ions 
which, attached to dust particles, may be transported to the clouds. 15 

Problems of cloud seeding technology and details of seeding deliv- 
ery methods are discussed in a later section of this chapter, as are 

14 Ibid., p. 156. 

15 Ibid., pp. 156-157. 


some proposed techniques for atmospheric modification that go beyond 
cloud seeding. 16 


The seeding of clouds to increase precipitation, either rainfall or 
snowfall, is the best known and the most actively pursued weather 
modification activity. Changes in clouds and precipitation in the 
vicinity of cloud seeding operations have shown unquestionaBly that 
it is possible to modify precipitation. There is evidence, however, 
that such modification attempts do not always increase precipitation, 
but that under some conditions precipitation may actually be de- 
creased, or at best no net change may be effected over an area. Never- 
theless, continued observations of clouds and precipitation, from both 
seeded and nonseeded regions and from both experiments and com- 
mercial operations, are beginning to provide valuable information 
which will be useful for distinguishing those conditions for which 
seeding increases, decreases, or has no apparent effect on precipita- 
tion. These uncertainties were summarized in one of the conclusions 
in a recent study on weather modification by the National Academy 
of Sciences : 17 

The Panel now concludes on the basis of statistical analysis of well-designed 
field experiments that ice-nuclei seeding can sometimes lead to more precipita- 
tion, can sometimes lead to less precipitation, and at other times the nuclei 
have no effect, depending on the meteorological conditions. Recent evidence has 
suggested that it is possible to specify those microphysical and mesophysical 
properties of some cloud systems that determine their behavior following 
artificial nucleation. 

Precipitation enhancement has been attempted mostly for two gen- 
eral types of cloud forms, both of which naturally provide precipita- 
tion under somewhat different conditions. Convective or cumulus 
clouds are those which are formed by rising, unstable air, brought 
about by heating from below or cooling in the upper layers. Under 
natural conditions cumulus clouds may develop into cumulo-nimbus 
or "thunderheads," capable of producing heavy precipitation. Cu- 
mulus clouds and convective systems produce a significant portion 
of the rain in the United States, especially during critical growing 
seasons. Attempts to augment this rainfall from cumulus clouds 
under a variety of conditions have been underway for some years 
with generally uncertain success. The other type of precipitation- 
producing clouds of interest to weather modifiers are the orographic 
clouds, those which are formed when horizontally moving moisture- 
laden air is forced to rise over a mountain. As a result of the cooling 
as the air rises, clouds form and precipitation often falls on the 
windward side of the mountain. Through seeding operations, there 
have been attempts to augment precipitation through acceleration 
of this process, particularly in winter, in order to increase mountain 

Figures 1 and 2 show regions of the coterminous United States 
which are conducive to precipitation management through seeding 
of spring and summer convective clouds and through seeding oro- 
graphic cloud systems, respectively. The principles of precipitation 

16 See pp. 115 and 129. 

17 National Academy of Sciences, National Research Council, Committee on Atmospheric 
Sciences, "Weather and Climate Modification : Problems and Progress," Washington, D.C., 
1973, p. 4. 


enhancement for both cumulus and orographic clouds, and the present 
state of knowledge and technology for such modification, are dis- 
cussed in the following sections. 

Figure 1. — Regions where preciptation management may be applied to enhance 
rainfall from spring and summer showers. 

Figure 2.— Regions where precipitation management may be applied to enhance 
snowfall from winter orographic weather systems, thus augmenting spring and 
summer runoff from mountain snowpacks. 


Currmlus clouds 

If air containing moisture is cooled sufficiently and if condensation 
nuclei such as dust particles are present, precipitation may be pro- 
duced. This process occurs when air is forced to rise by convection, 
so that the water vapor condenses into clouds. Cumulus clouds are the 
woolly vertical clouds with a flat base and somewhat rounded fop, 
whose origin can always be traced to the convection process. They can 
most often be observed during the summer and in latitudes of high 
temperature. When updrafts become strong under the proper con- 
ditions, cumulus clouds often develop into cumulonimbus clouds, the 
principal producer of precipitation. About three-fourths of the rain 
in the tropics and subtropics and a significant portion of that falling 
on the United States is provided from cumulus clouds and convective 

The science of cloud study, begun in the 1930's and greatly expanded 
following World War II, includes two principal aspects — cloud micro- 
physics and cloud dynamics. Though once approached separately by 
different groups of scientists, these studies are now merging into a 
single discipline. In cloud physics or microphysics the cloud parti- 
cles — such as condensation and freezing nuclei, water droplets, and ice 
crystals — are studied along with their origin, growth, and behavior. 
Cloud dynamics is concerned with forces and motions in clouds, the 
prediction of cloud structure, and the life cycle of updrafts and down- 
drafts. 18 

For cloud modification purposes, present theories of microphysical 
processes provide an ample basis for field seeding experiments ; how- 
ever, further work is still needed on laboratory experiments, improved 
instrumentation, and research on assumptions. On the other hand, 
the processes in cloud dynamics are not completely understood and 
require continued research. 19 

Most cumulus clouds evaporate before they have had opportunity 
to produce precipitation at the Earth's surface. In fact many clouds 
begin to dissipate at about the same time that rain emerges from their 
bases, leading to the impression that they are destroyed by the forma- 
tion of precipitation within them. This phenomenon is not yet fully 
understood. Cumulus clouds have a life cycle; they are born, mature, 
and eventually age and die. Small cumuli of the trade regions live only 
about 5 to 10 minutes, while medium-sized ones exist for about 30 min- 
utes. On the other hand, a giant cumulonimbus cloud in a hurricane 
or squall line may be active for one to several hours. In its lifetime it 
may exchange over 50 million tons of water, producing heavy rain, 
lightning, and possibly hail. At all times, however, a cumulus cloud 
struggles to exist; there is a precarious balance between the forces 
aiding its growth and its destruction. 20 

The increasing capability to simulate cloud processes on the com- 
puter has been a major advance toward understanding cloud modifi- 
cation. The ways in which cloud microphysics influences convective 

18 Simpson Joanne and Arnett S. Dennis, "Cumulus Clouds and Their Modification. In 
Wilmot N. Hess (ed.), "Weather and Climate Modification." New York, John Wiley & Sons, 

^'^Mo'schandreas, Demetrios J . and Irving Leichter. "Present Capabilities to Modify 
Cumulus Clouds." Geomet. Inc. report No. EF-46.H. Final report for U.S. Navy Environ- 
mental Prediction Research Facility, Mar. :U), 1976. p. 209. . 

20 Simpson and Dennis, "Cumulus Clouds and Their Modification, 1947, pp. 234-23o. 


dynamics are not well documented or modeled, however. Feedback 
mechanisms are dynamic and thermodynamic. Dynamically, the buoy- 
ancy is reduced by the weight of the particles formed within the 
cloud, sometimes called "water loading/' Modeling suggests that 
thermodynamic feedback from the microphysics can be even more 
important, as evaporation at the edges of the cloud produces cooling 
and thus induces downdrafts. Observations confirm this important 
influence of evaporation, particularly where the cloud environment is 
relatively dry, but the effect is minimized in humid tropical regions. 21 

Cumulus modification experiments 

An enormous amount of energy is expended in natural atmospheric 
processes. As much energy as the fusion energy of a hydrogen super- 
bomb is released in a large thunderstorm, and in a moderate -strength 
hurricane the equivalent of the energy of 400 bombs is converted each 
clay. In his attempt to modify precipitation from clouds, man must 
therefore look for some kind of a trigger mechanism by which such 
energetically charged activities can be controlled, since he cannot hope 
to provide even a fraction of the energy involved in the natural proc- 
ess. A major problem in evaluating modification efforts is the large 
natural variability in atmospheric phenomena. A cumulus cloud can, 
in fact, do almost anything all by itself, without any attempt to mod- 
ify its activity by man. This high variability has led the layman to 
overestimate grossly what has been and can be done in weather modifi- 
cation. In designing an experiment, this variability requires that there 
be sound statistical controls. 22 

Precipitation is formed by somewhat different processes in warm 
clouds and in subfreezing clouds. In the former, droplets are formed 
from condensation of water vapor on condensation nuclei and grow 
through collision and coalescence into raindrops. In subfreezing 
clouds, such as the cumuli under discussion, supercooled water drop- 
lets are attached to ice nuclei which grow into larger ice particles. 
When large enough, these particles fall from the cloud as snow or sleet 
or may be converted to rain if the temperature between the cloud and 
the Earth's surface is sufficiently warm. Increasing precipitation 
through artificial means is more readily accomplished in the case of 
the subfreezing clouds. In addition, attempts have been made to pro- 
mote the merging of cumulus clouds in order to develop larger cloud 
systems which are capable of producing significantly more precipita- 
tion than would be yielded by the individual small clouds. 

Nearly all cumulus experiments have involved "seeding" the clouds 
with some kind of small particles. Sometimes the particles are dis- 
persed from the ground, using air currents to move them into the 
clouds. Most often the materials are dispensed from aircraft, by releas- 
ing them upwind of the target clouds, by dropping them into the cloud 
top, by using the updraft from beneath the cloud, or by flying through 
the cloud. Although more expensive, aircraft seeding permits more 
accurate targeting and opportunity for measurements and observa- 
tions. In the Soviet Union, cumulus clouds have been seeded success- 

21 Simpson. Joanne, "Precipitation Augmentation from Cumulus Clouds and Systems : 
Scientific and Technical Foundations." 1975. Advances in Geophysics, vol. 19. Xew York. 
Academic Press, 1976. pp. 10-11. 

122 Simpson and Dennis, "Cumulus Clouds and Their Modification," 1974, pp. 240-241. 


fully with artillery shells and rockets, using radar to locate parts of 
the clouds to be seeded. 23 

Augmentation of precipitation in cumulus clouds has been attempted 
both by accelerating the coalescence process and by initiating ice parti- 
cle growth in the presence of supercooled water. In fact, these processes 
are essentially identical in cumuli where the tops extend above the 
freezing level. 

Prior to the 1960's nearly all supercooled seeding experiments and 
operations were concerned with attempting to increase precipitation 
efficiency, based on consideration of cloud microstructure. 24 This is 
essentially a static approach, intended to produce precipitation by in- 
creasing the total number of condensation nuclei, through the intro- 
duction of artificial nuclei injected by seeding into or under the clouds. 
This approach has been moderately successful in convective storms 
with conducive cloud microstructure in a number of locations — Cali- 
fornia, Israel, Switzerland, and Australia — where clouds are often 
composed of small supercooled droplets, typical of winter convection 
and of continental air masses. 25 On the other hand, the large cumulus 
clouds originating in tropical and subtropical ocean regions, which are 
evident over much of the eastern United States during the summer, are 
much less influenced by this static approach. A technique known as 
dynamic seeding has shown promise in enhancing precipitation from 
clouds of this type. 

According to dynamic seeding philosophy, the strength, size, and 
duration of vertical currents within the cloud have stronger control on 
cumulus precipitation than does the microstructure. In this technique, 
first demonstrated in the 1960 ? s, the seeding provides artificial nuclei 
around which supercooled water freezes, liberating large quantities of 
latent heat of fusion, within the clouds, causing them to become more 
buoyant and thus to grow to greater heights. This growth invigorates 
circulation within the cloud, causes increased convergence at its base, 
fosters more efficient processing of available moisture, and enhances 
rainfall through processes by which cumuli ordinarily produce such 
precipitation. Results of the Florida Area Cumulus Experiment 
(FACE) , conducted by the U.S. Department of Commerce, seem to in- 
dicate that dynamic seeding has been effective in increasing the sizes 
and lifetimes of individual cumuli and the localized rainfall resulting 
from them. 20 

Success thus far in rain enhancement from dynamic seeding of 
cumulus has been demonstrated through seeding techniques applied 
to single, isolated clouds. In addition to the experiments in Florida, 
dynamic seeding of single clouds has been attempted in South Dakota, 
Pennsylvania, Arizona, Australia, and Africa, with results similar to 
those obtained in Florida. 27 It appears, however, that a natural process 
necessary for heavy and extensive convective rainfall is the merger 
of cloud groups. Thus, this process of cloud merger must be promoted 
in order for cloud seeding to be effective in augmenting rainfall from 

23 Ibid., p. 242. 

24 Ibid., 1974, pp. 246-247. 

25 Ibid., p. 247. , - „ 

26 William L. Woodley. Joanne Simpson. Ronald Biondini, and Joyce Berkeley. "Rainfall 
Results. 1970-I97. r > ; Florida Area Cumulus Experiment," Science, vol. ID'S. No. 4280. Feb. 2f>. 
1077. p. 735. 

-~ Simpson and Dennis, "Cumulus Clouds and Their Modification." 1974, p. 261. 


cumulus clouds. The FACE experiment has been designed to investi- 
gate whether dynamic seeding can induce such cloud merger and in- 
creased rainfall. 28 Area wide cumulus cloud seeding experiments are 
also planned for the U.S. Department of the Interior's High Plains 
Cooperative program (HIPLEX), being conducted in the Great 
Plains region of the United States. 29 30 There has been some indication 
that desired merging has been accomplished in the Florida experi- 
ment. 31 Though this merging and other desirable effects may be 
achieved for Florida cumulus, it must be established that such mergers 
can also be induced for other connective systems which are found over 
most of the United States east of the Great Plains. Changnon notes 
that, "The techniques having the most promise for rain enhancement 
from convective clouds have been developed for single, isolated types 
of convective clouds. The techniques have been explored largely 
through experimentation with isolated mountain-type storms or with 
isolated semitropical storms. * * * Weather modification techniques 
do not exist for enhancing precipitation from the multicellular con- 
vective storms that produce 60 to 90 percent of the warm season 
rainfall in the eastern two-thirds of the United States." 32 

Effectiveness of precipitation enhancement research and operations 

A major problem in any precipitation enhancement project is the 
assessment of whether observed increases following seeding result from 
such seeding or occur as part of the fluctuations in natural precipita- 
tion not related to the seeding. This evaluation can be attempted 
through observations of physical changes in the cloud system which 
has been seeded and through statistical studies. 

Physical evaluation requires theoretical and experimental investi- 
gations of the dispersal of the seeding agent, the manner that seeding 
has produced changes in cloud microstructure, and changes in gross 
characteristics of a cloud or cloud system. Our understanding of the 
precipitation process is not sufficient to allow us to predict the magni- 
tude, location, and time of the start of precipitation. Hence, because 
of this lack of detailed understanding and the high natural variability 
of precipitation, it is necessary to use statistical methods as well. There 
is a closer physical link between seeding and observable changes in 
cloud microstructure ; however, even the latter can vary widely with 
time and position in natural, unseeded clouds, so that statistical evalua- 
tion is also required with regard to the measurement of these 
quantities. 33 

It should first be determined whether the seeding agent reached 
the intended region in the cloud with the desired concentration rather 

^Woodley, et al.. "Rainfall Results, 1970-1975; Florida Area Cumulus Experiment, 
1977. p. 735. 

29 Bureau of Reclamation. U.S. Department of the Interior. "High Plains Cooperative 
Program : Progress and Planning Report No. 2," Denver. March 1976. p. 5. 

30 The history, purposes, organization, and participants in the FACE and HIPLEX pro- 
grams are discussed along with other programs of Federal agencies in chapter o or tms 
report. _ . L „ 

31 William L. Woodley and Robert I. Sax. "The Florida Area Cumulus Experiment : Ka- 
tionale. Design. Procedures. Results, and Future Course." U.S. Department of Commerce. 
National Oceanic and Atmospheric Administration, Environmental Research Laboratories. 
NOAA technical report ERL 354-WMPO 6. Boulder, Colo., January 19 , 6 pp. 41-4o. 

32 Changnon, Stanley A.. Jr., "Present and Future of Weather Modification : Regional 

ISS33J Warn 9 e 7 r°'j PP '"Th 9 e ~Deteetabilitv of the Effects of Seeding." In World Meteorological Or- 
ganization. Weather Modification Programme, position papers used in the Preparation of 
the plan for the Precipitation Enhancement Experiment (PEP), Precipitation Enhancement 
Project Report No. 2. Geneva, November 1976, annex I, p. 43. 


than spreading into other areas selected as controls. When the agent 
has been delivered by aircraft, this problem is usually minimized, 
though even in this case, it is desirable to learn how the material has 
diffused through the cloud. When ground-based seeding generators 
are used, the diffusion of the material should be studied both by 
theoretical studies and by field measurements. Such measurements 
may be made on the seeding agent itself or on some trace material 
released either with the seeding agent or separately ; this latter might 
be either a fluorescent material such as zinc sulphide or any of various 
radioactive materials. Sometimes the tracer might be tracked in the 
cloud itself, while in other experiments it may be sufficient to track 
it in the precipitation at the surface. 34 

In looking for cloud changes resulting from seeding, the natural 
cloud behavior is needed as a reference; however, since the character- 
istics of natural clouds vary so widely, it is necessary to observe a 
number of different aspects of the properties and behavior of seeded 
clouds against similar studies of unseeded clouds in order to be able 
^o differentiate between the two. It is further desirable to relate such 
behavior being studied to predictions from conceptual and numerical 
models, if possible. Direct observations should be augmented by radar 
studies, but such studies should substitute for the direct measurements 
only when the latter are not possible. 35 

A statistical evaluation is usually a study of the magnitude of the 
precipitation in the seeded target area in terms of its departure from 
the expected value. The expected quantity can either be determined 
from past precipitation records or through experimental controls. Such 
controls are established by dividing the experimental time available 
roughly in half into periods of seeding and nonseeding, on a random 
basis. The periods may be as short as a day or be 1 or 2 weeks in dura- 
tion. The precipitation measured during the unseeded period is used as 
a measure of what might be expected in the seeded periods if seeding 
hadn't occurred. In another technique, control areas are selected where 
precipitation is highly correlated with that in the target area but 
which are never seeded. The target area is seeded on a random basis 
and its rainfall is compared with that of the control area for both 
seeded and unseeded periods. Another possibility includes the use of 
two areas, either of which may be chosen for seeding on a random basis. 
Comparisons are then made of the ratio of precipitation in the lirst 
area to that in the second with the first area seeded to the same ratio 
when the second is also seeded. There are many variations of these 
basic statistical designs, the particular one being used in a given experi- 
ment depending on the nature of the site and the measuring facilities 
available. As with the seeding techniques employed and the physical 
measurements which are made, experimental design can only be final- 
ized after a site has been selected and its characteristics studied. 36 

Results achieved through cumulus modification 

Cumulus modification is one of the most challenging and controver- 
sial areas in weather modification. In some cases randomized seeding 
efforts in southern California and in Israel have produced significant 

Ibid., p. 44. 
33 Ibid. 

M Ibid., p. 47). 


precipitation from bands of winter cyclonic storms. However, attempts 
have been less promising in attributing increased rain during summer 
conditions to definitive experiments. There has been some success in 
isolated tropical cumuli, where seeding has produced an increase in 
cloud height and as much as a twofold to threefold increase in rain- 
fall. 37 

In the Florida area cumulus experiment (FACE), the effects on 
precipitation over a target area in southern Florida as a result of 
seeding cumuli moving over the area is being studied under the spon- 
sorship of the National Oceanic and Atmospheric Administration 
(NOAA). Analysis of the data from 48 days of experimentation 
through 1975 provided no evidence that rainfall over the fixed target 
area of 13,000 square kilometers had been altered appreciably from 
dynamic seeding. On the other hand, there is positive evidence for 
increased precipitation from seeding for clouds moving through the 
area. 38 

When FACE data from the 1976 season are combined with previous 
data, however, increasing the total number of experimental days to 75, 
analysis shows that dynamic seeding under appropriate atmospheric 
conditions was effective in increasing the growth and rain production 
of individual cumulus clouds, in inducing cloud merger, and in pro- 
ducing rainfall increases from groups of convective clouds as they 
pass through the target area. A net increase seemed to result from the 
•seeding when rainfall on the total target area is averaged. 39 

Further discussion of FACE purposes and results is found under 
the summary of weather modification programs of the Department of 
Commerce in chapter 5. 40 

Recent advances in cumulus cloud modification 

In the past few years some major advances have been achieved in 
cumulus experimentation and in improvement of scientific under- 
standing. There has been progress in (1) numerical simulation of 
cumulus processes and patterning; (2) measurement techniques; (3) 
testing, tracing, delivery, and targeting of seeding materials; and (4) 
application of statistical tools. Recognition of the extreme difficulty of 
cumulus modification and the increased concept of an overall systems 
approach to cumulus experimentation have also been major advances. 41 

Orographic clouds and precipitation 

In addition to the convection clouds, formed from surface heating, 
clouds can also be formed when moist air is lifted above mountains 
as it is forced to move horizontally. As a result, rain or snow may fall, 
and such precipitation is said to be orographic, or mountain induced. 
The precipitation results from the cooling within the cloud and charac- 

37 Sax. R. I.. S. A. Changnon. L. O. Grant. W. F. Hitschfeld. P. V. Hobbs. A. M. Kanan. 
and J. Simnson, "Weather Modification: Where Are We Now and Where Should \\ e Be 
Going? An Editorial Overview." Journal of Applied Meteorology, vol. 14. No. o, August 1975, 
P- 662. 

38 Woodlev, et al., "Rainfall Results, 1970-1975 ; Florida Area Cumulus Experiment. 
1977. p. 742. , „ . . 

^Woodley. William L.. Joanne Simpson. Ronald Biondini. and Jill Jordan. NOAA s 
Florida Area Cumulus Experiment; Rainfall Results. 1970-1976 " In preprints from the 
Sixth Conference on Planned and Inadvertent Weather Modification, Champaign, 111.. 
Oct. 10-13. 1977. Boston, American Meteorological Society, 1977, p. 209. 

40 gee p 292 

41 Sax. et.' ai. "Weather Modification : Where Are We Now and Where Should We Be 
Going? An Editorial Overview," 1975, p. 663. 


teristically falls on the windward side of the mountain. As the air 
descends on the leeward side of the mountain, there is warming and 
dissipation of the clouds, so that the effect of the mountains is to pro- 
duce a "rain shadow" or desert area. The Sierra Nevada in western 
North America provide such conditions for orographic rain and snow 
along the Pacific coast and a rain shadow east of the mountains when 
moisture laden air generally flows from the Pacific eastward across 
this range. 

The western United States is a primary area with potential for 
precipitation augmentation from orographic clouds. This region re- 
ceives much of its annual precipitation from orographic clouds during 
winter, and nearly all of the rivers start in the mountains, deriving 
their water from melting snowpacks. The major limitation on agricul- 
ture here is the water supply, so that additional water from increased 
precipitation is extremely valuable. Streamflow from melting snow 
is also important for the production of hydroelectric power, so that 
augmentation of precipitation during years of abnormally low natural 
snowfall could be valuable in maintaining required water levels neces- 
sary for operation of this power resource. Orographic clouds provide 
more than 90 percent of the annual runoff in many sections of the 
western United States. 42 

Figure 3 (a) and (b) are satellite pictures showing the contrast 
between the snow cover over the Sierra Nevada on April 28, 1975, and 
on April 19, 1977. This is a graphical illustration of why much of Cali- 
fornia was drought stricken during 1977. The snowpack which custo- 
marily persists in the highest elevations of the Sierras until July had 
disappeared by mid-May in 1977. 43 

The greatest potential for modification exists in the winter in this 
region, while requirements for water reach their peak in the summer ; 
hence, water storage is critical. Fortunately, the snowpack provides a 
most effective storage, and in some places the snowmelt lasts until early 
July. Water from the snowmelt can be used directly for hydroelectric 
power generation or for irrigation in the more arid regions, while 
some can be stored in reservoirs for use during later months or in sub- 
sequent dry years. In some regions where the snowpack storage is not 
optimum, offseason orographic precipitation is still of great value, 
since the water holding capacity of the soil is never reached and addi- 
tional moisture can be held in the soil for the following groAving season. 

Orographic clouds are formed as moist air is forced upward hy 
underlying terrain. The air thus lifted, containing water vapor, cools 
and expands. If this lifting and cooling continue, the air parcels will 
frequently reach sal mat ion. If the air becomes slightly supersaturated, 
small droplets begin to form by condensation, and a cloud develops, 
which seems to hang over the mountain peak. The location where this 
condensation occurs can be observed visually by the edge of the cloud 
on the windward side of the mountain. Upon descent in the lee of the 
mountain the temperature and vapor capacity of the air parcel again 

"Grant, Lewis O. and Archie M. Kahan, "Weather Modification for Augmenting Oro- 
graphic Precipitation." In Wilmot N. Hess (editor), "Weather and Climate Modification," 
New York. Wiley. 1974. p. 2S5. 

4:1 U.S. Department of Commerce, news release, NOAA 77-234. NO A A Public Affairs Office, 
Rockville, Md., Aug. 17, 1077. 


increase, so that any remaining liquid droplets or ice crystals 
evaporate. 44 

(a) April 28, 1975 

Figure 3. — NOAA-3 satellite pictures of the snowcover on the Sierra Nevada 
Mountains in (a) April 1975 and (b) April 1977. (Courtesy of the National 
Oceanic and Atmospheric Administration.) 

44 Sax. et al.. "Weather Mortification : Where Are We Now and Where Should We Be 
Going?" an editorial overview, 1975, pp. 657-658. 



(b) April 19, 1977 

The supercooled cloud droplets exist as liquid at temperatures down 
to about -20° C ; but at temperatures colder than -20° C, small ice 
crystals begin to form around nuclei that are naturally present in the 
atmosphere. Once formed, the ice crystals grow rapidly because the 
saturation vapor pressure over ice is less than that over water. As the 
crystals increase they may fall and eventually may reach the ground 
as snow. The temperature at the top of the cloud is an important 
factor in winter storms over mountains, since natural ice crystals will 
not form in large quantities if the cloud top is warmer than —20° C. 
If the temperature is below —20° C, however, a large fraction of the 
cloud particles will fall as snow from natural processes. 45 

45 Weisbecker, Leo W. (compiler), "The Impacts of Snow Enhancement; Technology 
Assessment of Winter Orographic Snowpack Augmentation in the Upper Colorado River 
Basin," Norman, Okla., University of Oklahoma Press, 1974, pp. 64-66. 


Orographic precipitation modification 

According to Grant and Kalian, " * * * research has shown that 
orographic clouds * * * provide one of the most productive and 
manageable sources for beneficial weather modification." 46 In a re- 
cent study by the National Academy of Sciences, it was concluded 
broadly that orographic clouds provide one of the "main possibilities 
of precipitation augmentation,*' based on the considerations below : 47 
A supply of cloud water that is not naturally converted into 
precipitation sometimes exists for extended periods of time ; 

Efficient seeding agents and devices are available for treating 
these clouds; 

Seeding agents can sometimes (not always) be delivered to 
the proper cloud location in proper concentrations and at the 
proper time; 

Microphysical cloud changes of the type expected and neces- 
sary for seeding have been demonstrated; 

Substantial increases in precipitation with high statistical sig- 
nificance have been achieved in some well-designed randomized 
experiments for clouds that, based on physical concepts, should 
have seeding potential; and 

Augmentation of orographic precipitation can have great eco- 
nomic potential. 

Although natural ice crystals will not form in sufficient numbers if 
the cloud top is warmer than —20° C, it has been shown that particles 
of silver iodide smoke will behave as ice nuclei at temperatures some- 
what warmer than — 20° C, so that ice crystals can be produced by such 
artificial nuclei in clouds with temperatures in the range of —10° to 
— 20° C. Whereas in the natural state, with few active nuclei at these 
temperatures, the cloud particles tend to remain as water droplets, 
introduction of the silver iodide can quickly convert the supercooled 
cloud into ice crystals. Then, the natural growth processes allow the 
crystals to grow to sufficient size for precipitation as snow. 48 

Meteorological factors which favor increased snowfall from oro- 
graphic clouds through cloud seeding are summarized by 
Weisbecker : 49 

The component of the airflow perpendicular to the mountain 
ridge must be relatively strong. 

The air must have a high moisture content. Generally, high 
moisture is associated with above-normal temperatures. 

The cloud, including its upper boundary, should be at a temp- 
erature warmer than — 20° C. Since temperature decreases with 
increasing altitude, this temperature criterion limits the altitude 
of the cloud top. However, it is advantageous for the cloud base 
to be low, since the water droplet content of the cloud will then 
be relatively large. 

46 Grant and Kahan, "Weather Modification for Augmenting Orographic Precipitation," 
1974. p. 282. 

* 7 Committee on Climate and Weather Fluctuations and Agricultural Production, National 
Research Council, "Climate and Food ; Climatic Fluctuation and U.S. Agricultural Produc- 
tion." National Academy of Sciences. Washington, D.C., 1976, p. 136. 

48 Weisbecker, "The Impacts of Snow Enhancement ; Technology Assessment of Winter 
Orographic Snowpack Augmentation in the Upper Colorado Basin," 1974, p. 66. 

» Ibid. pp. 66-67. 


It must be possible to disperse silver iodide particles within the 
cloud in appropriate numbers to serve as ice crystal nuclei. If 
ground generators are used, the silver iodide smoke must be dif- 
fused by turbulence and lifted by the airflow into cloud regions 
where temperatures are colder than — 10° C. 

The ice crystals must have time to grow to a precipitable size 
and to fall to Earth before reaching the downdrafts that exist on 
the far side of the mountain ridge. 
The meteorological conditions which are ideally suited for augment- 
ing artificially the snowfall from a layer of orographic clouds are 
depicted in figure 4. The figure also shows the optimum location of 
ground-based silver iodide smoke generators upwind of the target area 
as well as the spreading of the silver iodide plume throughout the cloud 
by turbulent mixing. Although there are several seeding agents with 
suitable properties for artificial ice nuclei, silver iodide and lead iodide 
appear to be most effective. Owing to the poisonous effects of lead com- 
pounds, lead iodide has not had wide use. The optimum silver iodide 
particle concentration is a function of the temperature, moisture, and 
vertical currents in the atmosphere ; it appears to be in the range from 
5 to 100 nuclei per liter of cloud. 50 While the most common means of 
dispersing silver iodide in mountainous areas is by ground-based gen- 
erators, other methods of cloud seeding make use of aircraft, rockets, 
and balloons. 

In contrast to convective clouds, ice crystal formation in orographic 
clouds is thought to be static, depending primarily on cloud micro- 
physics, and that orographic cloud seeding has little effect on the 
general patterns of wind, pressure, and temperature. On the other 
hand, clouds formed primarily by convection, such as summer cumulus 
or hurricane clouds, are believed to be affected dynamically by seeding 
as noted above in the discussion of modification of convective clouds. 51 
Since the lifting of the air in winter mountain storms is mainly caused 
by its passage over the mountain barrier, the release of latent energy 
accompanying this lifting has little effect upon the updraft itself. In 
convective cases, however, heat released through seeding increases 
buoyancy and lifting, with attendant effects on the wind and pressure 
fields. The static nature of the processes involved in orographic cloud 
modification therefore suggests that there is less chance that the storm 
dynamics downwind of the target area will be altered appreciably as a 
result of the modification activities. 52 

60 Ibid., p. 68. 

si See p. 68. 

52 Ibid., pp. 70-71. 


Figure 4. — Idealized model showing meteorological conditions that should lead 
to increased snowfall if clouds are seeded with silver iodide particles. (From 
Weisbecker, 1974.) 

Orographic seeding experiments and seeddbility criteria 

A randomized research weather modification program with winter 
orographic storms in central Colorado was initiated by Colorado State 
University in 1959. Data on precipitation and cloud physics were col- 
lected for 16 years under this Climax program, named for the location 
of its target area near Climax, Colo. Analysis of data has shown pre- 
cipitation increases between 100 and 200 percent when the average 
temperatures of seeded clouds at the 500 millibar level were — 20°C or 
warmer. When corresponding temperatures were — 26°C to — 21°C, 
precipitation changes ranged between —5 and +6 percent. For tem- 
peratures colder than — 26°C, seeded cloud systems produced decreases 
in precipitation ranging from 22 to 46 percent. 53 

While the results of Climax have provided some useful guidelines in 
establishing seedability criteria of certain cloud systems, it has been 
learned from other experimental programs that direct transfer of the 
Climax criteria to other areas is not warranted. 54 In particular, this 
nontransferability has been evident in connection with analysis of re- 
sults from the Colorado River Basin Pilot Project, conducted from 
1970 through 1975 in the San Juan Mountains of southwest Colorado, 
sponsored by the Bureau of .Reclamation of the U.S. Department of 
the Interior. 55 

Difficulties are frequently encountered in attempting to evaluate ex- 
perimental cloud-seeding programs. A major problem in assessing 
results of all cold orographic cloud-seeding projects stems from the 
high natural variability of cloud properties. Frequent measurements 
are therefore required in order to monitor these properties carefully 
and consistently throughout the experiment. Another set of problems 
which have troubled investigators in a number of experimental pro- 
grams follow from improper design. Such a deficiency can easily re- 

53 Hjermstad. Lawrence M.. "San Juan and Climax." In proceedings of Special Weather 
Modification Conference; Augmentation of Winter Orographic Precipitation in the West- 
ern United States, San Francisco, Nov. 11-13, 1975, Boston, American Meteorological 
Society. 1975, p. 1 (abstract). 

~ 4 Ibid., pp. 7-S. . ... 

53 This nroiect. part of Project Skywater of the Bureau of Reclamation, is discussed along 
with other programs of Federal agencies in chapter 5 of this report, see p. 2o4. 

34-857 O - 79 - 8 


suit, for example, if insufficient physical measurements have been taken 
prior to establishment of the design of the experiment. 56 

Under Project Sky water the Bureau of Reclamation has carried out 
an analysis of data from seven past weather modification projects in 
order to identify criteria which define conditions when cloud seeding 
will increase winter snowfall in mountainous terrain and when such 
seeding would have no effect or decrease precipitation. The seven 
projects examined in the study were conducted in the Rocky Moun- 
tains, in the Sierra Nevada, and in the southern coast range in Cali- 
fornia during the 1960's and 1970 ? s, in areas which represent a wide 
range of meteorological and topographical conditions. 57 

Figure 5 shows the locations of the seven projects whose results were 
analyzed in the Skywater study, and table 5 includes more detailed 
information on the locations and dates of seeding operations for these 
projects. General seedability criteria derived from this study were 
common to all seven projects, with the expectation that the criteria 
will also be applicable to all winter orographic cloud-seeding projects. 
While there have been other efforts to integrate results from several 
projects into generalized criteria, based only on a few meteorological 
variables, Vardiman and Moore considered 11 variables which depend 
on mountain barrier shapes and sizes and on characteristics of the 
clouds. Some of these variables are physically measurable while others 
are derived from simple computations. 58 

Figure 5. — Locations of winter orographic weather modification projects whose 
results were used to determine generalized cloud seeding criteria. (From Vardi- 
man and Moore, 1977. 

M Hobbs. Peter V, "Evaluation of Cloud Seeding Experiments; Some Lessons To Be 
i.earned From the Cascade and San Juan Projects." In proceedings of Special Weather 
Modification Conference ; Augmentation of Winter Orographic Precipitation in the West- 
Society 1976 . af Francisco, Nov. 11-13, 1975. Boston, American Meteorological 

"Vardiman. Tarry and James A. Moore. "Generalized Criteria for Seeiing Winter Oro- 
graphic Cloudy' Skywater monograph No. 1, U.S. Department of the Interior, Bureau of 
133 -Division of Atmospheric Water Resources Management, Denver, July 1977. 

■ Ibid., p. 15. 



[From Vardiman and Moore, 1977] 

Project Site Seeding operations 


Bridger Range Project (BGR) Rocky Mountains, Montana 1969-70 to 1971-72 (3 seasons). 

Climax Project (CMX) Rocky Mountains, Colorado 1960-61 to 1969-70 (10 seasons). 

Colorado River Basin Pilot Project Rocky Mountains, Colorado 1970-71 to 1974-75 (5 seasons). 


Central Sierra Research Experiment Sierra Nevada, California 1968-69 to 1972-73 (5 seasons). 


Jemez Mountains Project (JMZ) Rocky Mountains, New Mexico 1968-69 to 1971-72 (4 seasons). 

Pyramid Lake Pilot Project (PYR) Sierra Nevada, California/Nevada 1972-73 to 1974-75 (3 seasons). 

Santa Barbara Project (SBA) Southern Coast Range, California 1967-68 to 1973-74(7 seasons). 

Detailed analyses were conducted on four variables calculated from 
topography and vertical distributions of temperature, moisture, and 
winds. These are (1) the stability of the cloud, which is a measure of 
the likelihood that seeding material will reach a level in the cloud 
where it can effect the precipitation process; (2) the saturation mixing 
ratio a£ cloudbase, a measure of the amount of water available for 
conversion to precipitation; (3) the calculated cloud top temperature, 
a measure of the number of natural ice nuclei available to start the 
precipitation process; and (4) the calculated trajectory index, a meas- 
ure of the time available for precipitation particles to form, grow, and 
fall to the ground. 59 

Results of the study thus far are summarized below : 

Seeding can increase precipitation at and near the mountain crest under the 
following conditions: 

Stable clouds with moderate water content, cloud top temperatures between 
—10 and —30° C, and winds such that the precipitation particles would be 
expected to fall at or near the crest of the mountain barrier. 

Moderately unstable clouds with moderate-to-high water content, cloud 
top temperatures between —10 and —30° C, and a crest trajectory for the pre- 

Seeding appears to decrease precipitation across the entire mountain barrier 
under the following condition: 

Unstable clouds with low water content, cloud top temperatures less 
than —30° C, and winds such that the precipitation particles would 
be carried beyond the mountain crest and evaporate before reaching the 

59 Bureau of Reclamation. Division of Atmospheric Water Resources Management, "Sum- 
mary Report ; Generalized Criteria for Seeding Winter Orographic Clouds.'" Denver. March 
1977, p. 1. (This is a summary of the report by Vardiman and Moore which is referenced 
above. ) 

80 Ibid., pp. 1-2. 

Rime ice conditions at sensing device which measures intensity of snowfall. 
(Courtesy of the Bureau of Reclamation.) 


Results quoted above represent only a portion of the analyses which 
are to be carried out. Seeding "window" bounds must be refined, and 
the expected effect must be converted into estimates of additional pre- 
cipitation a target area might experience during a winter season. It is 
very unlikely that observed effects could have occurred by chance in 
view of the statistical tests which were applied to the data. 61 

Operational orographic seeding projects 

For several decades commercial seeding of orographic clouds for 
precipitation augmentation has been underway in the western United 
States, sponsored by specific users which include utility companies, 
agricultural groups, and State and local governments. Much of the 
technology was developed in the late forties and early fifties by com- 
mercial operators, with some improvements since. The basic technique 
most often used involves release of silver iodide smoke, usually from 
ground-based generators, along the upwind slopes of the mountain 
where clouds are seeded, as shown schematically in figure 6. It is the 
opinion of Grant and Kahan that this basic approach still appears 
sound for seeding orographic clouds over many mountain barriers, but 
that in all aspects of these operating programs, there have been "sub- 
stantial improvements" as a result of research and development pro- 
grams. 62 They summarized the following major deficiencies of past 
operational orographic seeding programs : 

1. The lack of criteria for recognizing the seedability of specific 

2. The lack of specific information as to where the seeding 
materials would go once they are released. 

3. The lack of specific information as to downwind or broader 
social and economic effects from the operations. 

4. The lack of detailed information on the efficiency of seeding 
generators and material being used for seeding clouds with differ- 
ing temperatures. 63 

Figure 6. — Schematic view of silver iodide generators placed upwind from a tar- 
get area in the mountains, where orographic clouds are to be seeded for pre- 
cipitation enhancement (From Weisbecker, 1974.) 

61 Ibid., p. 2. 

63 Grant and Kalian, "Weather Modification for Augmenting Orographic Precipitation," 
1974, p. 307. 

« Ibid., pp. 307-308. 


Results achieved through orographic precipitation modification 

Results from several projects in the western United States have 
shown that winter precipitation increases of 10 to 15 percent are pos- 
sible if all suitable storms are seeded. 64 From randomized experiments 
at Climax, Colo., precipitation increases of 70 to 80 percent have been 
reported. These results, based on physical considerations, are repre- 
sentative of cases which have a high potential for artificial 
stimulation. 65 

64 U.S. Department of the Interior, Bureau of Reclamation, "Reclamation Research in the 
Seventies," Second progress report. A water resources technical publication research report 
No. 28, Washington, U.S. Government Printing Office, 1977, p. 2. 

65 National Academy of Sciences, "Climate and Food ; Climatic Fluctuation and U.S. Agri- 
cultural Production," 1976, p. 136. 




The hail problem 

Along with floods, drought, and high winds, hail is one of the major 
hazards to agriculture. Table 6 shows the estimated average annual 
hail loss for various crops in the United States, for each of the 18 
States whose total annual crop losses exceed $10 million. Also included 
in the table are total losses for each crop and for each of the 18 States 
and the aggregate of the remaining States. 

The following vivid description of a hailstorm conveys both a sense 
of its destructiveness and some notion of its capricious nature : 

At the moment of its happening, a hailstorm can seem a most disastrous event. 
Crashing stones, often deluged in rain and hurled to the surface by wind, can 
create instant destruction. Picture windows may he broken, cars dented, or a 
whole field of corn shredded before our eyes. 

Then quite quickly, the storm is over. Xow the damage is before us. we per- 
ceive it to be great, and we vow to do something to prevent its happening again. 

But what we have experienced is "our" storm. Hail did not happen perhaps a 
mile away. We may see another the same day. or never again. Thus, the concept 
of hail suppression is founded in a real or perceived need, but the assessment of 
this solution must be considered in terms of the nature of hail. 06 


[In millions of dollars] 1 



and veg- 







grains 2 






































North Dakota. 







North Carolina 
















South Dakota 










































South Carolina 











. 1 


















Other States 


















1 1973 production and price levels. 

2 Coarse grains: Barley, rye, oats, sorghum. 

Source: "National Hail Research Experiment" from Boone (1974). 

A major characteristic of hail is its enormous variability in time, 
space, and size. Some measure of this great variability is seen in figure 
7, which shows the average annual number of days with hail at points 
within the continental United States. The contours enclose points with 
equal frequency of hail days. 67 

00 Chanson, Stanley A.. Jr.. Ray Jay Davis, Barbara C. Farhar. J. Eupene Haas, J. 
Lorena Ivens. Marvin V. Jones, Donald A. Klein, Dean Mann. Griffith M. Morgan. Jr.. Steven 
T. Sonka. Earl R. Swanson. C. Robert Taylor, and Jon Van Blokland. "Hail Suppression : 
Impacts and Issues." Final report — "-Technology Assessment of the Suppression of Hail 
fTASH ) ." Urbana, 111.. Illinois State Water Survey. April lt>77 (sponsored by the National 
Science Foundation, Research Applied to National Needs Program), p. 9. 

« Ibid. 


Hail forms in the more active convective clouds, with large vertical 
motions, where large quantities of water vapor condense under condi- 
tions in which large ice particles can grow quickly. The kinds of con- 
vective clouds from which hail can be formed include (1) supercells 
(large, quasi-steady-state, convective storms, (2) multicell storms 
(active convective storms with multiple cells), (3) organized convec- 
tive storms of squall lines or fronts, and (4) unstable, highly convective 
small cumuli (primarily occurring in spring). 68 While hail generally 
occurs only in thunderstorms, yet only a small proportion of the world's 
thunderstorms produce an appreciable amount of hail. Based upon sev- 
eral related theories, the following desciption of the formation of hail 
is typical : 

Ice crystals or snowflakes, or clumps of snowflakes, which form above the 
zone of freezing during a thunderstorm, fall through a stratum of supercooled 
water droplets (that is, water droplets well below 0° O). The contact of the ice 
or snow particles with the supercooled water droplets causes a film of ice to form 
on the snow or ice pellet. The pellet may continue to fall a considerable distance 
before it is carried up again by a strong vertical current into the stratum of 
supercooled water droplets where another film of water covers it. This process 
may be repeated many times until the pellet can no longer be supported by the 
convective updraft and falls to the ground as hail. 69 

( Note: The lines enclose points (stations) that have equal frequency of hail days ) 

Figure 7. — Average annual number of days with hail at a point, for the contiguous 
United States. (From Changnon, et al., TASH, 1977.) 

68 National Academy of Sciences, "Climate and Food ; Climatic Fluctuation and U.S. 
Agricultural Production." 1976. p. 141. 

89 Koeppe. Clarence E. and George C. de Long, "Weather and Climate," New York, Mc- 
Graw-Hill, 1958, pp. 79-80. 


Modification of hail 

According to D. Ray Booker, "Hail modification seeding has been 
done operationally for decades in the high plains of the United States 
and in other hail prone areas of the world. Thus, there appears to be a 
significant market for a hail-reduction technology." 70 In the United 
States most attempts at hail suppression are conducted by commercial 
seeders who are under contract to State and county governments and to 
community associations. There are also extensive hail suppression op- 
erations underway in foreign countries. Although some successes are 
reported, many important questions are still unanswered with regard 
to mitigation of hail effects, owing largely to lack of a satisfactory 
scheme for evaluation of results from these projects. 

In theory, it should be possible to inhibit the formation of large 
ice particles which constitute hailstones by seeding in order to increase 
the number of freezing nuclei so that only smaller ice particles will 
develop. This would then leave the cloud with insufficient precipita- 
tion water to allow the accretion of supercooled droplets and the 
formation of hail of damaging size. This simplistic rationale, how- 
ever, does not provide insight into the many complications with 
which artificial nail suppression is fraught ; nor does it explain the 
seemingly capricious responses of hailstorms to seeding and the incon- 
sistent results which characterize such modification attempts. As with 
all convective systems, the processes involved are very complex. They 
are controlled by the speed of movement of the air parcels and precipi- 
tation particles, leading to complicated particle growth, evaporation, 
and settling processes. 71 As a result, according to Changnon, the con- 
clusions from various hail suppression programs are less certain than 
from those for attempts to enhance rain from convective clouds, and 
they are best labeled "contradictory." 72 

Changnon identifies two basic approaches that have been taken 
toward hail modification : 

»Most common has been the intensive, high rates of seeding of the potential 
storm with silver iodide in an attempt to transform nearly all of the super- 
cooled water into ice crystals, or to "glaciate" the upper portion of the clouds. 
However, if only part of the supercooled water is transformed into ice, the 
storm could actually be worsened since growth by accretion is especially rapid 
in an environment composed of a mixture of supercooled drops and ice crystals. 
Importantly, to be successful, this frequently used approach requires massive 
seeding well in advance of the first hailstone formation. 

The second major approach has been used in the Soviet Union and * * * in the 
National Hail Research Experiment in Colorado. It involves massive seeding 
with silver iodide, but only in the zone of maximum liquid water content of the 
cloud. The hope is to create many hailstone embryos so that there will be in- 
sufficient supercooled water available to enable growth to damaging stone sizes." 

70 Booker, D. Ray, "A Marketing Approach to Weather Modification," background paper 
prepared for the U.S. Department of Commerce Weather Modification Advisory Board. 
Feb. 20, 1977. p. 4. 

i National Academy of Sciences, "Climate and Food; Climatic Fluctuation and U.S. 
Agricultural Production." 1070. p. 143. 

72 Changnon, "Present and Future of Weather Modification ; Regional Issues," 1975, 
p. 102. 

™ Ibid. 


Precipitation instrument site, including, from left to right, hailcube, anemom- 
eter, rain/hail separator, and Belfort weighing precipitation gage. (Courtesy of 
the National Science Foundation. ) 

Hail seeding technologies 

The most significant field programs in hail suppression during recent 
years have included those conducted in the Soviet Union, in Alberta, 
in South Africa, and in northeastern Colorado (the National Hail 
Research Experiment). In the course of each of these projects, some 
of which are still underway, various procedural changes have been 
initiated. In all of them, except that in South Africa, the suppression 
techniques are based on increasing the number of hail embryos by 


seeding the cloud with ice nuclei. Usually, the seeding material is 
silver iodide, but the Russians also use lead iodide, and on occasion 
other agents such as sodium chloride and copper sulfate have been 
used. The essential problems in seeding for hail suppression are re- 
lated to how, when, and where to get the seeding agent into potential 
hail clouds and how to identify such clouds. 74 

Soviet suppression techniques are based on their hypothesis that 
rapid hail growth occurs in the "accumulation zone," just above the 
level of maximum updraft, where liquid water content can be as 
great as 40 grams per cubic meter. To get significant hail, the maximum 
updraft should exceed 10 to 15 meters per second, and the temperature 
in this zone must be between and —25° C. Upper large droplets 
freeze and grow, combining with lower large droplets, and an increase 
in particle size from 0.1 cm to 2 or 3 cm can occur in only 4 to 5 minutes. 
In the several Russian projects, the seeding agent is introduced at 
selected cloud heights from rockets or antiaircraft shells ; the number 
of volleys required and the position of injection being determined by 
radar echo characteristics and past experience in a given operational 
region. 75 

In other hail suppression projects, seeding is most frequently carried 
out with aircraft, from which flares containing the seeding agent are 
released by ejection or dropping. Each flare may contain up to 100 
grams of silver iodide ; and the number used as well as the spacing and 
height of ignition are determined from cloud characteristics as well as 
past experience in a given experiment or operation. In each case it 
is intended to inject the seeding material into the supercooled portion 
of the cloud. 

Evaluation of hail suppression technology 

It appears that mitigation of the effects of hail has some promise, 
based on the collection of total evidence from experiments and opera- 
tions around the world. In the Soviet Union, scientists have been 
reporting spectacular success (claims of 60 to 80 percent reduction) 76 
in hail suppression for nearly 15 years; however, their claims are not 
universally accepted, since there has not been careful evaluation under 
controlled conditions. Hail-seeding experiments have had mixed results 
in other parts of the world, although a number of commercial seeders 
have claimed success in hail damage reduction, but not with convincing 
evidence. 77 

Successful hail suppression reports have come from a number of 
operational programs in the United States as well as from weather 
modification activities in the Soviet Union and in South Africa. Often 
the validity of these results is questionable in view of deficiencies in 
project design and data analysis; nevertheless, the cumulative evidence 
suggests that hail suppression is feasible under certain conditions. 
There are also reports of negative results, for example, in foreign pro- 
grams and in the National Hail Research Experiment in the United 

7 *Chan*rnon. Stanlev A.. Jr.. and Griffith M. Moroni. Jr.. "Desipn of an Experiment To 
Suppress Hail In Illinois." Illinois State Water Survey. TSWS/R 01 /7fi. RnHetln 01. State ot 
Illinois. Department of Registration and Education, Urbana, 1970. pp. 82-S3. 

75 Ibid., p. S3. 

70 Chancrnon. "Present and Future of Weather Modification," 107". p 102. 

77 Rattan. Louis J. statement submitted to Subcommittee on Environment and Atmos- 
phere Committee on Science and Technology, U.S. House of Representatives, at hearings. 
June 18, 1970, pp. 7-8. 


States, which indicate that under some conditions seeding induces 
increased hail. 78 

Atlas notes that this apparent dichotomy has until recently been 
attributed to different approaches to the techniques and rates of seed- 
ing. However, lie observes that both positive and negative results 
have been obtained using a variety of seeding methods, including 
ground- and cloud-based generators, flares dropped from above the 
cloud top, and injection by rockets and artillery. 79 In discussing the 
reasons for increased hail upon seeding, Atlas states : 

There are at least four physical mechanisms by which seeding may produce 
increased hail. Two of these occur in situations in which the rate of supply of 
supercooled water exceeds that which can be effectively depleted by the com- 
bination of natural and artificially produced hail embryos. This may occur in 
supercell storms and in any cold-base storm in which the embryos are graupel 
rather than frozen raindrops. Moreover, present seeding methods are much more 
effective in warm-base situations in which the hail embryos are frozen raindrops. 
Increased hail is also probable when partial glaciation of a cloud is produced 
and the hail can grow more effectively upon the ice-water mixture than upon 
the supercooled water alone. Similarly, increases in the amount of hail may 
occur whenever the additional latent heat resulting from nucleation alters the 
undraft profile in such a manner as to increase its maximum velocity or to 
shift the peak velocity into the temperature range from —20° to —30° C, where 
the accreted water can be more readily frozen. A probable associated effect is 
the redistribution of precipitation loading by the combination of an alternation 
in the updraft velocity and the particle sizes such that the hail embroyos may 
grow for longer durations in a more favorable growth environment. 80 

Surreys of hail suppression effectiveness 

Recently, Changnon collected information on the effectiveness of 
hail suppression technology from three different kinds of sources. One 
set of data was based on the results of the evaluations of six hail sup- 
pression projects; another was the collection of the findings of three 
published assessments of hail modification ; and the third was obtained 
from two opinion surveys conducted among weather modification 
scientists. 81 The principal statistics on the estimated capabilities for 
hail suppression from each of these groups of sources are summarized 
in table 7. Where available, the estimated change in rainfall accom- 
panying the hail modification estimates are also included. Such rain- 
fall changes might have been sought intentionally as part of a hail sup- 
pression activity or might result simply as a byproduct of the major 
thrust in reducing hail. In the table, a plus sign* indicates an estimated 
percentage increase in hail and/or rainfall while a minus sign signifies 
a percentage decrease. 

The six evaluations in part A of table 7 are from both experimental 
and operational projects, each of which was conducted for at least 3 
years in a single locale and in each of which aircraft seeding tech- 
niques were used. Thus, the results of a number of earlier experiments, 
using ground-based seeding generators, were not considered in the 
estimations. Furthermore, change in hail due to suppression activities 
was defined on the basis of crop-loss statistics rather than on the basis 
of frequency of hail days, since Changnon does not consider the latter, 

7S Atlas. David, "The Paradox of Hail Suppression," Science, vol. 195, No. 4274, Jan. 14. 
1977. p. 195. 
79 Ibid. 

60 Ibid., pp 195-196. 

81 Chanjrnon. Stanlev A.. Jr.. "On tbe Status of Hail Suppression." Bulletin of the Amer- 
ican Meteorological Society, vol. 58, No. 1, Jan. 1977, pp. 20-28. 


along with other criteria such as number and size of hailstones, hail 
mass, and radar echo characteristics, to be a reliable indicator. 82 Note 
that five of the six projects listed indicate a hail suppression capability 
ranging from 20 percent to 48 percent. Changnon notes, however, that 
most of these results are not statistically significant at the 5 percent 
level, but that most scientists would classify the results as "opti- 
mistic." 83 

Table 7— Status of Hail Suppression and Related Rainfall Modification 
(Based on information from Changnon. On the Status of Hail Suppression. 


1. Texas: Hail modification was —48 percent (crop-loss cost value) ; no change 
in rainfall. 

2. Southwestern North Dakota : Hail modification was —32 percent (crop-hail 
insurance rates) ; no rain change information available. 

3. North Dakota pilot project : Hail modification was —30 percent (a composite 
of hail characteristics, radar, and crop-loss data) ; change in rainfall was +23 

4. South Africa : Hail modification was —40 percent (crop-loss severity ; 
change in rainfall was —4 percent. 

5. South Dakota "Statewide" project : Hail modification was —20 percent 
(crop loss) ; increase in rainfall was +? percent. 

6. National hail research experiment in Colorado : 

Increase in hail mass was +4 percent to +23 percent, with median of 
+23 percent : 
Increase in rainfall was +25 percent. 


1. American Meteorological Society : Positive but unsubstantiated claims and 
growing optimism. 

2. National Academy of Sciences: 30 to 50 percent reductions in U.S.S.R. and 
15 percent decreases in France — neither result proven by experimentation. 

3. Colorado State University Workshop : 

—30 percent modification nationwide ; 

—30 percent modification in the High Plains, with ± 10-percent change in 
rain ; unknown results in the Midwest ; also unknown rainfall effects. 


1. Farhar-Grant questionnaire (214 answers) : —25 percent crop-hail damage 
nationwide, although majority — 59 percent — admit they do not know. 

2. Illinois State Water Survey questionnaire (63 answers) : 

—30 percent hail loss, with +15 percent rain increasein the Great Plains: 
—20 percent hail loss, with +10 percent rain increase in the Midwest. 

The results, shown in part B of table 7, from the recent published 
assessments of capability in hail suppression reveal a position of 
"guarded optimism;" however, there is no indication of definitive 
proof of hail suppression contained in those assessments. 84 These pub- 
lished assessments are comprised of a statement, on the status of 
weather modification by the American Meteorological Society, 85 the 
conclusions of a study on the progress of weather modification by the 

82 Ibid., p. 22. 
*»Th1rt.. p. 26. 
"* Ibid. 

" American Meteorological Society. "Policy Statement of tbo American Meteorological 
Rocietv on Purposeful and Inadvertent Modifier Hon of Woatbcr nnd Climate," Bulletin of 
tbo American Meteorological Society, vol. , r )4. No. 7, July 1073. pp. 694-695. 


National Academy of Sciences, 86 and a report on a workshop at Colo- 
rado State University on weather modification and 'agriculture. 87 

The third view (part C, table 7) resulting from two opinion surveys, 
indicates wide-ranging but basically "bipolar" attitudes among the 
scientists surveyed. The majority of the experts queried felt that a hail 
suppression capability could not be identified; however, a sizable 
minority were of the opinion that a moderate capability for modifying 
hail (greater than 20-percent decrease) does now exist. Changnon says 
that the results of these opinion surveys show at best that the con- 
sensus must be considered to be a pessimistic view of a hail suppres- 
sion capability. 88 

In his conclusions on the status of hail suppression technology, 
Changnon states : 

These three views of the current status of hail suppression, labeled as (1) opti- 
mistic, (2) slightly optimistic, and (3) pessimistic, reflect a wide range of opin- 
ion and results. Clearly, the present status of hail suppression is in a state of 
uncertainty. Reviews of the existing results from 6 recent operational and ex- 
perimental hail suppression projects are sufficiently suggestive of a hail sup- 
pression capability in the range of 20 to 50 percent to suggest the need for an 
extensive investigation by an august body of the hail suppression capability 
exhibited in these and other programs. 

One of the necessary steps in the wise experimentation and future use of hail 
suppression in the United States is to cast the current status in a proper light. 
This can only be accomplished by a vigorous in-depth study and evaluation of 
the results of the recent projects. 88 

Conclusions from the TASH study 

Sponsored by the Eesearch Applied to National Needs program of 
the National Science Foundation, a major technology assessment of 
hail suppression in the United States was conducted from 1975 through 
1977, by an interdisciplinary research team. 90 This Technology Assess- 
ment of the Suppression of Hail (TASH) study was intended to bring 
together all of the considerations involved in the application of hail 
suppression, in the present and in the future, to ascertain the net value 
of such technology to society. The goals of the study were : 

To describe the current knowledge of hail suppression. 
To identify long-range expectations for such a technology. 
To estimate the societal impacts that might be generated by its wide use. 
To examine public policy actions that would most equitably direct its beneficial 

From its interdisciplinary study of hail suppression and its impacts 
the TASH team reached the following broad conclusions on the effects 
of hail and on the potential technology for suppression of hail : 

The United States experiences about $850 million in direct crop and property 
hail losses each year, not including secondary losses from hail. The key character- 
istic of hail is its enormous variability in size, time, and space. 

Among the alternative ways of dealing with the hail problem, including crop 
insurance, hail suppression, given a high level of development, appears to be the 
most promising future approach in high hail loss areas. Economic benefits from 
effective hail suppression vary by region of the country, with the most benefit to 

66 National Academy of Sciences. National Research Council. Committee on Atmospheric 
Sciences. "Weather and Climate Modification : Problems and Progress," Washington, D.C., 
1973. pp. 100-106. 

87 Grant and Reid, "Workshop for an Assessment of the Present and Potential Role of 
Weather Modification in Agriculture Production." 1975. pp. 33-45. 

88 Changnon. "On the Status of Hail Suppression," 1977, p. 26. 
68 Ibid., pp. 26-27. 

90 Changnon. et al.. "Hail Suppression ; Impacts and Issues." Technology Assessment of 
the Suppression of Hail (TASH) , 1977, 432 pp. 


be derived in the Great Plains area. Any alterations in rainfall resulting from 
hail suppression would importantly affect its economic consequences. 

The effects of cloud seeding on rainfall are more significant than its effects on 
hail from economic and societal standpoints. 

At the present time there is no established hail suppression technology. It may 
be possible to reduce damaging hail about 25 percent over the growing season in a 
properly conducted project. 

Reducing the scientific uncertainties about hail suppression will require a sub- 
stantial commitment by the Federal Government for long-term funding of a sys- 
tematic, well-designed program of research. For the next decade or so, monitoring 
and evaluation of operational programs will be important. 

Benefit-cost analysis revealed that investment in development of the high-level 
technology would result in a ratio of 14 :1, with the present value of benefits esti- 
mated to total $2.8 billion for 20 years. The low-level technology showed a nega- 
tive benefit-cost ratio. Research and development to provide the high-level 
technology is the best choice from an economic standpoint; a minimal level of 
support would be nonbeneficial. In a word, if we are going to develop hail suppres- 
sion technology, we would need to do it right. 

Effective hail suppression will, because of the hail hazard, technological 
approach, patterns of adoption, and institutional arrangements, lead to regionally 
coherent programs that embrace groups of States, largely in the Great Plains. 

Some would gain and others would lose from widespread application of an 
effective hail suppression technology. Farmers within adopting regions would 
receive immediate benefits from increased production. After several years this 
economic advantage would be diminished somewhat, but increased stability of 
income would remain. Farmers growing the same crops outside the adopting areas 
would have no advantages and would be economically disadvantaged by commod- 
ity prices lower than they would have been with no hail suppression. The price 
depressing effects result from increased production in adopting areas. Consumers 
would benefit from slightly decreased food prices. The impacts generated by a 
highly effective technology include both positive and negative outcomes for vari- 
ous other stake-holder groups in the Nation. For the Nation as a whole, the 
impacts would be minor and beneficial. On balance, the positive impacts outweigh 
the negative impacts if a high-level technology can be developed. 

An adequate means of providing equitable compensation on an economically 
sound basis for persons suffering from losses due to cloud seeding has not been 
developed. Some better procedure for compensating losers will be necessary. In 
addition, present decision mechanisms and institutional arrangements are inade- 
quate to implement the technology in a socially acceptable manner. Some mecha- 
nism for including potential opponents in the decisionmaking process will be 

It is unlikely that widespread operational hail suppression programs would 
have serious adverse environmental impacts, although lack of sufficient knowledge 
indicates that adverse impacts should not be ruled out. Long-term environmental 
effects are not known at the present time. 91 


Fog poses a hazard to man's transportation activities, particularly 
to aviation, where as a result of delays air carriers lose over $80 million 
annually. Highway accidents attributed to fog are estimated to cost 
over $300 million per year. 92 Most often the impetus to develop effec- 
tive fog and stratus cloud dispersal capabilities has come from the 
needs of commercial and military aircraft operations. 

There are two basic kinds of fog, and the suppression of each re- 
quires a different approach. Supercooled fog and stratus clouds are 
comprised of liquid water droplets whose temperature is below f reez- 

81 Farhar. Barbara C, Stanley A. Changnon, Jr., Earl R. Swanson, Ray J. Davis, and 
J Eugene Haas. "Hail Suppression and Societv. Summary of Technology Assessment of Hail 
Suppression," Urbana. 111.. "Illinois State Water Survey, June 1977." pp. 21-22. (This 
document is an executive summary of the technology assessment by Changnon, et al., "Hail 
Suppression ; Impacts and Issues.") 

92 National Oceanic and Atmospheric Administration, "Summary Report : Weather Modi- 
fication ; Fiscal Years 1969, 1970, 1971," Rockville, Md., May 1973, p. 72. 


ing (i.e., 0° C or below). Supercooled fogs account for only about 5 
percent of all fog occurrences in the United States, although they are 
prevalent in certain parts of northeastern and northwestern North 
America. The remainder of North American fogs are warm fogs (water 
droplets warmer than 0° C). 93 Although cold fog has been amenable 
to modification, so that there essentially exists an operational tech- 
nology for its dissipation, practical modification of warm fogs, on an 
economical basis, has not yet been achieved. 

Cold fog modification 

Dispersal of cold fog by airborne or ground-based techniques has 
been generally successful and has become an operational weather modi- 
fication technology. In the United States cold fog dispersal operations 
have been conducted, for example, by commercial airlines, usually with 
dry ice as the seeding agent. The U.S. Air Force has also operated 
ground-based liquid propane systems, at domestic and foreign bases, 
which have been effective in dissipating cold fog over runways, thus 
reducing flight delays and diversions. 94 Conducted largely at airports, 
cold fog suppression is usually accomplished using aircraft, which drop 
various freezing agents, such as dry ice or silver iodide as they fly over 
the fog-covered runways. The agents initiate ice crystal formation and 
lead to precipitation of the growing crystals. 95 Ground-based systems 
for cold fog dispersal have also been used and have some advantages 
over airborne systems. Such a system can operate continuously for ex- 
tended time periods more economically and more reliably. 

Warm fog modification 

The remainder of North American fogs are "warm fogs" for which 
a suitable dispersal capability remains to be developed. Crutchfield 
summarizes the status of warm fog dispersal technology and its eco- 
nomic potential : 

The much more extensive warm fogs which cause delays, accidents, and costly 
interruptions to every type of transportation have proved intractable to weather 
modification thus far. Some success has been achieved on occasion by heavy 
seeding with salt and other materials, but results have not been uniformly good, 
and the materials used have presented environmental problems in the areas 
treated. Heating airport runways has been of some benefit in dealing with warm 
fog, but at present is not generally effective in cost-benefit terms and can inter- 
rupt air traffic. 

Nevertheless, the research and technology problems involved in the dispersal 
of warm fog appear to be of manageable proportions, and the benefits from an 
environmentally acceptable and predictable technique for dealing with warm 
fog would be of very real interest in terms of economic gain. 96 

A number of field techniques have been attempted, with some meas- 
ure of success, for artificial modification of warm fogs. Seeding is 
one technique, where the seeding agents are usually hygroscopic parti- 
cles, solution drops, or both. There are two possible desired effects of 
seeding warm fogs, one being the evaporation of fog droplets, resulting 
in visibility improvement. A second desired effect of seeding, results 
from the "coalescence" process, in which the solution droplets, falling 

93 Changnon, "Present and Future of Weather Modification," 1975, p. 165. 

94 National Oceanic and Atmospheric Administration "Summary Report : Weather Modi- 
fication ; Fiscal Year 1973." Rockville, Md., December 1974, pp. 39-40. 

9a Changnon. "Present and Future of Weather Modification," 1975. p. 165. 

98 Crutchfield, James A., "Weather Modification : The Economic Potential." Paper prepared 
for U.S. Department of Commerce Weather Modification Advisory Board. University of 
Washington, Seattle, May 1977, pp. 5-6. 

34-857 O - 79 - 9 


through the fog layer, collect the smaller fog droplets, increasing 
visibility as the fog particles are removed in the fallout. 97 There is a 
wide diversity of hygroscopic particles which can and have been used 
for warm fog dissipation. Sodium chloride and urea are the most 
common, but others have included polyelectrolyte chemicals, an ex- 
ceedingly hygroscopic solution of ammonium-nitrate urea, and some 
biodegradable chemicals. Seeding particle size is critical to the effec- 
tiveness of a warm fog dispersal attempt ; it has been found that poly- 
dispersed particles (i.e., material with a distribution of particle sizes) 
are more effective in inducing fog modification than are extra fine 
particles of uniform size, which were only thought to be optimum in 
earlier experiments. Other problems which are the subject of con- 
tinuing study relate to the seeding procedures, including the number 
of flights, number of aircraft to be used, and flight patterns in 
accordance with the local terrain and wind conditions. One of the 
most difficult operational problems in the seeding of warm fog is that 
of targeting. One solution to this problem, suggested by the Air Force, 
is the implementation of wide-area seeding instead of single-line 
seeding, which is so easily influenced by turbulence and wind shear. 98 
Another technique for dissipation of warm fog makes use of heating. 
The physical principle involved is the vaporization of the water drop- 
lets through introduction of sufficient heat to vaporize the water and 
also warm the air to such a temperature that it will hold the additional 
moisture and prevent condensation. Knowing the amount of liquid 
water in the atmosphere from physical measurements, the necessary 
amount of heat energy to be injected can be determined. 99 The fea- 
sibility of this approach was first demonstrated in England during 
World War II, when it was necessary to fly aircraft in all kinds of 
weather in spite of frequent fogbound conditions in the British Isles. 
The acronym FIDO, standing for Fog Investigations Dispersal Of, 
was applied to a simple system whereby fuel oil in containers placed 
along the runways was ignited at times when it was necessary to land 
a plane in the fog. Although burning as much as 6,000 gallons of oil 
for a single airplane landing was expensive and inefficient, it was 
justified as a necessary weather modification technique during war- 
time. 99 * 

Initial and subsequent attempts to disperse fog by burning liquid 
fuel were found to be hazardous, uneconomical, and sometimes in- 
effective, and, as a result, not much was done with this heating tech- 
nique until the French revised it, developing the Turboclair method 
for dissipating fog by heating with underground jet blowers. After 10 
years of development and engineering testing, the system was tested 
successfully by the Paris Airport Authority at Orly Airport. This 
program has given a new interest and stimulated further research and 
development of this technique both in the United States and elsewhere. 
In the United States, the Air Force conducted Project Warm Fog 
to test the effectiveness of heating to remove warm fog. It is clear that 
this method is promising; however, further studies are needed. 1 

97 Mosohnndreas. Demetrlos J., "Present Capabilities to Modify Warm Fog and Stratus," 
Geomet. Inc.. report No EF-300. Technical report for Office of Naval Research and Naval 
Air Svstems Command, Rockvllle, Md., Jan, 18, 1974, p. 13. 

88 Ibid., pp. 16-17. 

" Ibid pp. 24. 30. 

Halacy, Daniel S., Jr., "The Weather Changers," New York, Harper and Row. 1968, 
pp. 105-107. 

1 Moschandreas. "Present Capabilities to Modify Warm Fog and Stratus," 1974, pp. 


Research and development on warm fog dispersal systems has con- 
tinued under sponsorship of the U.S. Air Force, using both passive 
heat systems, and thermokinetic systems which combine both heat and 
mechanical thrust. A thermokinetic system, known as the Warm Fog 
Dispersal System (WFDS), consists of three components: The com- 
bustors, the controls, and the fuel storage and distribution hardware. 
Testing of the WFDS by the Air Force is to be conducted during late 
1978 and 1979 at Otis Air Force Base in Massachusetts, after which it 
is to be installed and operational at an Air Force base by 1982. 2 Dis- 
cussion of the Air Force development program and of the concurrent 
studies and interest on the Federal Aviation Administration in this 
thermokinetic fog dispersal system is found in chapter 5 of this report. 3 

There have been attempts to evaporate warm fogs through mechani- 
cal mixing of the fog layer with warmer, drier air from above. Such 
attempts have been underway using the strong downwash from heli- 
copters ; however, such a technique is very costly and would likely be 
employed only at military installations where a number of helicopters 
might be available. 

The helicopters hover or move slowly in the dry air above the fog 
layer. Clear dry air is moved downward into the fog by the circulation 
of the helicopter rotors. The mixture of dry and cloudy air permits the 
fog to evaporate, and in the fog layer there is created an opening whose 
size and lifetime are determined by the meteorological conditions in 
the area, by the flight pattern, and by the kind of helicopter. 

Conclusions reached by scientists involved in a series of joint U.S. 
Air Force- Army research projects using helicopters for fog dispersal 
follow : 

The downwash method by a single helicopter can clear zones 
large enough for helicopter landing if the depth of the fog is less 
than 300 feet (100 meters) . 

Single or multiple helicopters with flight patterns properly 
orchestrated can maintain continuous clearings appropriate for 
aircraft takeoff and landing in fogs of less than 300 feet (100 
meters) deep. 4 

In addition to the more commonly applied experimental techniques, 
such as seeding, heating, and mechanical mixing, other attempts have 
been made to disperse warm fogs. These have included the injection of 
ions or charged drops into the fog and the use of a laser beam to clear 
the fog. Further research is needed before definitive results can be 
cited using these methods. 5 

Table 8 is a summary of research projects on warm fog dispersal 
which had been conducted by various organizations in the United 
States between 1967 and 1973. Note that, in addition to field experi- 
ments, research included modeling, field measurements and observa- 
tions of fog, chamber tests, statistical interpretation, model evaluation, 
and operational assessment. 

On the basis of his study of research projects through 1973 and 
claims projected by the scientists involved in the various warm fog 

8 Kunkel. Bruce A., "The Design of a Warm Fog Dispersal System." In preprints of the 
Sixth Conference on Planned and Inadvertent Weather Modification. Champaign, 111.. 
Oct 10-13. 1977. Boston, American Meteorological Society, 1977, pp. 174-176. 

3 See pp. 305 and 308. 

4 Moschandreas, "Present Capabilities To Modify Warm Fog and Stratus," 1974, p. 45. 
6 Ibid., p. 14. 


modification programs, Demetrios Moschandreas formulated the fol- 
lowing conclusions on warm fog dispersal : 

Seeding with hygroscopic particles has been successful; how- 
ever, targeting problems would require the wide-area approach to 
seeding. Urea has also been projected as the agent which is most 
effective and least harmful to the environment. 

The heating technique is very promising and very efficient; 
studies for further verification of its capabilities are in order. 

The helicopter technique by itself has not been as promising as 
the combination of its use with hygroscopic seeding. 

Studies on the other less often used techniques have not reached 
the stage of wide field application. 

Numerical modeling has provided guidelines to the field experi- 
ments and insights to the theoretical studies of fog conditions. 

The laboratory experiments have given the scientists the con- 
trolled conditions necessary to validate a number of theories. The 
unique contribution of chamber tests to a better understanding of 
the dynamics of fog formation has been widely recognized. 6 


THROUGH 1973 « 

[From Moschandreas, 1974] 

Area of effort 

Year of publication 

1967 2 







Modeling and numerical ex- 





















Field measurements; fog ob- 















Chamber tests 






Field experiments 












Statistical interpretation 


Assessment of operational 







i Research is listed by agency conducting the research, or sponsoring it, when reporting its contractor's efforts; or by 
contractor's name when contractor's report is principal reference; individual researchers are not listed because these 
change, even though the cont ; mjity of effort is maintained. 

s Work reported prior to 1967 is not included here. 

Key: CAL— Cornell Aeronautical Laboratory, Inc.; AFCRL— Air Force Cambridge Research Laboratories; GEOMET— 
GEOMET, Inc.; MRI— Meteorology Research, Inc.; NWRF— U.S. Navy Weather Research Facility; EPRF— U.S. Navy En- 
vironmental Research Facility; EG&G— EG&G Environmental Services Ooeration; FAA— Federal Aviation Administra- 
tion: NCAR— National Center for Atomospheric Research; NWC— Naval Weapons Center; USNPGS— U.S. Naval Postgrad- 
uate School. 


At any given time over the whole Earth there are about 2,000 thun- 
derstorms in progress, and within these storms about 1,000 cloud-to- 
ground discharges are produced each second. 7 Lightning is essentially 
a long electric spark, believed to be part of the process by which an 
electric current is conducted from the Earth to the ipnosphere, though 

- 1H1U., pp. W^— »0. I, XT 

7 National Science Board. "Patterns and Perspectives In Environmental Science, Na- 
tional Science Foundation, Washington, D.C.. 1972, p. 157. 


the origin of the lightning discharge is still not fully understood. In 
fair weather the atmosphere conducts a current from the positively 
charged ionosphere to the ground, which has a negative charge. 

The details of the charge-generating process within a thunderstorm 
are not well understood, though theories have been proposed by cloud 
physicists. Probably a number of mechanisms operate together to bring 
about cloud electrification, though, essentially, the friction of the air 
on the water droplets and ice crystals in the storm strips off electrons 
which accumulate near the base of cumulonimbus clouds, while posi- 
tive charge collects in the upper part. The negative charge near the 
cloud base induces a local positive charge on the Earth's surface be- 
neath, reversing the normal fair weather situation. When the electri- 
cal potential between the cloud and ground becomes sufficiently large, 
an electrical discharge occurs, in which electrons flow from the cloud 
to the ground. In addition, there are discharges between clouds and 
between oppositely charged portions of the same cloud. 

In the rapid sequence of events which comprise a lightning stroke, 
the initial, almost invisible, flow of electrons downward from cloud 
to Earth, called the leader, is met by an upward-moving current of 
positive charges, establishing a conducting path of charged particles. 
A return stroke, much larger, then rushes from the ground to the 
cloud. All of these events appear as a single flash since they occur in 
about fifty microseconds; however, while most people perceive the 
lightning stroke as travelling from cloud to ground, it is actually the 
return stroke which provides the greatest flash. 8 

In the United States, lightning kills about 200 people annually, a 
larger toll than that caused by hurricanes. Since 1940, about 7,000 
Americans have lost their lives from lightning and related fires. 9 These 
casualties occur most often singly or occasionally two at a time, so that 
they are not nearly so newsworthy as are the multiple deaths and 
dramatic property damage associated with hurricanes, tornadoes, and 
floods. On the other hand, a lightning problem affecting large areas 
is the ignition of forest fires, some 10,000 of which are reported each 
year in the United States, where the problem is most acute in the 
Western States and Alaska. 10 Such fires inflict damage on commercial 
timber, watersheds, scenic beauty, and other resources, causing an 
estimated annual damage cost of $100 million. 11 Other examples in 
which lightning can be especially dangerous and damaging include 
discharges to aircraft and spacecraft and effects on such activities as 
fuel transfer operations and the handling of explosives. 

Because of the relative isolation of personal accidents due to light- 
ning, the only feasible controls over loss of life are through implemen- 
tation of safety measures which prevent exposure or by protection 
of relatively small areas and structures with lightning arresters. For- 
ested areas, however, require large area protection from lightning- 
caused fires in order to promote sound forest management. It is hoped 

8 Anthes. Richard A., Hans A. Panofsky, John C. CaMr, and Albert Rango, "The Atmos T 
phere," Columbus. Ohio. Charles E. Merrill. 1975, p. 174. 

9 U.S. Department of Commerce, "Peak Period for Lierhtniner Nears ; NOAA Lists Safety 
Rules." News Release NOAA 77-156. Washington. DC. June 19. 1977, p. 1. 

10 Fuquay. Donald M., "Lightning Damage and Lightning Modification Caused by Cloud 
Seeding." In Wilmot N. Hess (ed.), "Weather and Climate Modification," New York, John 
Wiley & Sons, 1974, p. 605. 

"Ibid., p. 604. 


that the widespread damage to forest resources resulting from the 
lightning-fire problem can be alleviated through use of weather modi- 
fication techniques. 

Lightning modification 

General approaches to lightning suppression through weather mod- 
ification, which have been contemplated or have been attempted, in- 
clude : 

Dissipation of the cloud system within which the thunderstorm 
originates or reduction of the convection within the clouds so that 
vigorous updrafts and downdrafts are suppressed. 

Reduction of the number of cloud-to-ground discharges, es- 
pecially during critical fire periods. 

Alteration of the characteristics of discharges which favor 
forest fuel ignition. 

Use of other weather modification techniques to produce rains 
to extinguish fires or to decrease the probability of ignition 
through increase of ambient relative humidity and fuel moisture. 
Lightning is associated with convective clouds; hence, the most 
direct suppression method would involve elimination of the clouds 
themselves or of the convection within them. Removal of the clouds 
would require changes to gross properties such as temperature insta- 
bility and moisture content of the air ; thus, such modification is not 
technically, energetically, or economically feasible. However, it might 
be possible to reduce somewhat the convection within the clouds. 12 

The formation of convective clouds depends on the upward motion 
of moist air caused by thermal instability and the subsequent produc- 
tion of water through cooling. This condensation releases more heat, 
which, in turn, causes further buoyancy and rising of the cloud. At 
these heights the temperature is low enough that the water can freeze, 
releasing more latent heat and enabling the cloud particles to rise 
even higher. As a result of the presence of nuclei which are naturally 
present in the cloud, glaciation proceeds continuously. Through arti- 
ficial nucleation, by seeding, natural glaciation may be reinforced and 
development of the cloud assisted. Rapid, premature seeding, how- 
ever, would still promote buoyancy but could also introduce so much 
turbulence that the cloud is unable to develop, because colder air en- 
tering the cloud by turbulent mixing would lower the changes of the 
cloud reaching moderate altitudes. Since there is a high correlation 
between cloud height, convective activity, and lightning, such early 
nucleation of a cloud should reduce the likelihood of intense elec- 
trical activity. Seeding would be accomplished by releasing silver 
iodide into the cores of growing cumulus clouds ; it could be delivered 
from ground dispensers or from aircraft into the updraft under the 
cloud base. The amount of seeding material must be chosen carefully, 
and, in order to increase the chances for cloud dissipation, overseed- 
ing is probably most effective, though such overseeding will also tend 
to reduce precipitation. On the other hand, rainfall may be advan- 
tageous for other purposes, including its inhibiting lightning-caused 
forest fires by providing moisture to the forest fuel. Consequently, the 
advantages which might be achieved through reducing cloud con- 

13 Stow, C. D.. "On the Prevention of Lightning," Bulletin of the American Meteorological 
Society, vol. 50, No. 7, July 1969, p. 515. 


vection and its attendant electrical activity must be weighed against 
the possible advantages lost through reduced precipitation. 13 

A more efficient lightning-suppression approach might involve in- 
terference with the processes which bring about charge separation in 
the cloud. At least five different mechanisms by which cloud electrifica- 
tion is established have been theorized, and possibly all or most of these 
mechanisms are active in any given situation, although on different 
occasions it is likely that some are more effective than others, depend- 
ing on meteorological conditions and geographical locations. 14 Data 
are as yet insufficient for determining which mechanisms will predomi- 
nate. It is not considered likely that a single treatment method would 
suffice to suppress all lightning activity through prevention of charge 
buildup, though it is conceivable that a given treatment may be capable 
of suppressing more than one charge-generating process. 15 In addition 
to glaciation of the cloud by overseeding (described above in connec- 
tion with convection reduction), accumulation of charge can be in- 
hibited through seeding with various chemicals which affect the 
freezing of water. Another technique uses seeding with a conducting 
chaff (very fine metalized nylon fibers), which increases conductivity 
between oppositely charged regions of the- storm and keeps the electric 
field from building up to the lightning-discharge level. The chaff fibers 
are of the type that have been used for radar "jamming," which can be 
dispensed underneath a thunderstorm from an aircraft. Experiments 
have shown this attempt at lightning suppression to have some 
promise. 16 

Although reduction in the number of cloud-to-ground discharges 
through cloud seeding would undoubtedly be instrumental in de- 
creasing the total number of forest fires, ignition is also influenced by 
such factors as the type of discharge, surface weather conditions, the 
terrain-fuel complex, and the influence of preceding weather on fuel 
moisture. The kind of discharge most frequently causing forest fires 
has been observed and its characteristics have been measured. Observa- 
tions indicate that ignition is most often caused by hybrid cloud-to- 
ground discharges having long continuing current phases, whose 
duration exceeds 40 milliseconds and that the probability of ignition is 
proportional to the duration of the continuing current phase. 17 

Evaluation of lightning suppression technology 

Seeding experiments to date have yielded results which suggest that 
both the characteristics and the frequency of lightning discharges have 
been modified. The physical processes by which lightning is modified 
are not understood ; however, basic physical charging processes have 
been altered through massive overseeding with silver iodide freezing 
nuclei. Direct measurements of lightning electricity have also shown 
that lightning strokes which contain a long continuing current are 
probably responsible for most lightning-ignited forest fires. Keduction 
of the duration of the long continuing current discharge through wea- 
ther modification techniques may, therefore, be more significant in 

13 Ibid. 

" Ibid., pp. 516-519. 
16 Ibid , p 519 

" Kasemir. Heinz W.. "Lightning Suppression by Chaff Seeding and Triggered Light- 
ning." In Wilmot N. Hess (editor), "Weather and Climate Modification," New York, Wiley. 
1974, N pp. 612-622. n a . „ . B „ 

"Fuquav, "Lightning Damage and Lightning Modification Caused by Cloud Seeding, 
1974, p. 606. 


reducing forest fires than reduction of the total amount of lightning 
produced by storms. 

From experiments in lightning suppression carried out under Proj- 
ect Skyfire by the U.S. Forest Service of the Department of Agricul- 
ture between 1965-67. Fuquay summarizes the following specific re- 
sults, based on a total of 26 individual storms (12 seeded and 14 
unseeded) : 18 

Sixty-six percent fewer cloud-to-ground discharges, 50 percent 
fewer intracloud discharges, and 54 percent less total storm light- 
ning occurred during seeded storms than during the not-seeded 

The maximum cloud-to-ground flash rate was less for seeded 
storms : over a 5-minute interval, the maximum rate averaged 8.8 
for not-seeded storms and 5 for seeded storms; for 15-minute in- 
tervals, the maximum rate for not-seeded storms averaged 17.7 
and 9.1 for seeded storms. 

The mean duration of lightning activity for the not-seeded and 
seeded storms was 101 and 64 minutes, respectively. Lightning 
duration of the not-seeded storms ranged from 10 to 217 minutes, 
while that of seeded storms ranged from 21 to 99 minutes. 

There was no difference in the average number of return strokes 
per discrete discharge (4.1 not-seeded versus 4 seeded) ; however, 
a significant difference was found for hybrid discharges (5.6 not- 
seeded versus 3.8 seeded) . 

The average duration of discrete discharges (period between 
first and last return stroke) decreased from 235 milliseconds for 
not seeded storms to 182 milliseconds for seeded storms. 

The average duration of continuing current in hybrid dis- 
charges decreased from 187 milliseconds for not-seeded storms to 
115 milliseconds for seeded storms. 
In a recent Federal appraisal of weather modification technology 
it was concluded that results of field experiments to suppress light- 
ning through silver iodide seeding have been ambiguous. 19 Although 
aim lysis of data previously obtained is continuing, the experimental 
seeding program of the Forest Service has been terminated. In more 
recent experiments, thunderstorms have been seeded from below 
with chaff (very fine metalized nylon fibers). Based on an analysis of 
10 chaff-seeded thunderstorms and 18 unseeded control storms, the 
number of lightning occurrences during the seeded storms was about 
25 percent of those observed in the control storms. This observed differ- 
ence was statistically significant even though the experiments were 
not strictly randomized. 20 

Experiments in lightning modification through cloud seeding have 
given results showing that, in some cases, lightning can be modified 
in a beneficial manner. From these results and the measured charac- 
teristics of lightning strokes, a hypothesis of lightning modification is 
being developed. There has been progress in identifying significant cor- 
relations between occurrence of lightning and such variables as storm 

u Fuquav. "Lightning Damage and Lightning Modification Caused by Cloud Seeding," 
1974, p. 6li. 

19 U.S. Domestic Council, Environmental Resources Committee, Subcommittee on Climate 
Change, "The Federal Role in Weather Modification." Washington, D.C., December 1975. 
p. 10. 



size, updraft characteristics, precipitation rates, and hail occurrence. 
According to Fuquay, such early successes ought not obscure the mag- 
nitude of the research yet required in order to identify and quantify 
the degree and applicability of lightning modification to the lightning- 
fire problem. 21 He also warns that : 

Until more is known about the adverse effects of seeding incipient thunder- 
storms, unexpected and adverse effects must be considered, although improved 
numerical models that accurately predict cloud development and the effects of 
seeding should minimize the risk of unexpected events. 22 


Severe storms have a greater immediate impact on human life and 
property than most other weather phenomena. A major portion of 
losses due to natural disasters results from two of the most destructive 
kinds of severe storms — hurricanes and tornadoes. During an average 
year the U.S. mainland is threatened by 8 tropical slorms and experi- 
ences over 600 tornadoes. 23 Among the results of the annual devastation 
from these storms are the loss of hundreds of lives and the accumula- 
tion of hundreds of millions of dollars in property damage. 

Perhaps the most important problems to be attacked in weather 
modification are associated with the abatement of severe storms. While 
rainfall augmentation promises borderline economic value at best, al- 
ternatives which can contribute more significantly to severe water 
shortages may prove more suitable. On the other hand, the annual 
threat of tolls in damages and fatalities from hurricanes and tornadoes 
will persist year after year, and research directed toward modification 
of these severe phenomena requires continued support. There have been 
dramatic attempts, with some successes, in demonstrating the potential 
reduction of the hazards of hurricanes ; however, almost no research 
has been directed toward tornado suppression. 


A hurricane is an intense cyclone which forms over tropical seas, 
smaller in size than middle-latitude cyclones, but much larger than a 
tornado or a thunderstorm. With an average size of 500 miles (800 
kilometers) in diameter, the hurricane consists of a doughnut-shaped 
ring of strong winds in excess of 64 knots which surrounds an area of 
extremely low pressure and calm at the storm's center, called the eye. 2 * 
The generic name for all vortical circulations originating over tropi- 
cal waters is "tropical cyclone." When fully developed with sufficiently 
strong winds, such storms are called hurricanes in the Atlantic and the 
eastern Pacific Oceans, typhoons in the northwest Pacific, baguios in 
the Philippines, Bengal cyclones in the Indian Ocean, and willy-willies 
near Australia. For a tropic cyclone whose winds are in the range of 
33 to 64 knots, the official name' in the United States is a tropical storm. 
The hurricane season is that portion of the year having a relatively 

21 Fuquay, "Lightning Damage and Lightning Modification Caused by Cloud Seeding," 
1974. p. 612. 

22 Ibid., p. 606. 

23 Feieral Coordinator for Meteorological Services and Supporting Research. "Federal 
Plan for Meteorological Services and Supporting Resenrch : Fiscal Year 1973." U.S. Depart- 
ment of Commerce, National Oceanic and Atmospheric Administration, Washington, D.C., 
January 1972. p. 1. 

24 Anthes, Richard A.. Hans A. Panofskv. -Tohn J. Cahir. and Albert Rango. "The Atmos- 
phere." Columbus, Ohio, Charles E. Merrill. 1975. p. 150. 


high incidence of hurricanes and usually is regarded as the period 
between June and November in the Northern Hemisphere. 25 

Owing to their duration, which exceeds that of earthquakes, and to 
their violence, which approaches that of tornadoes, hurricanes are the 
most destructive natural phenomena. Prior to Hurricane Agnes in 
1972, whose total damage exceeded $3 billion, the annual hurricane 
property losses in the United States amounted to about $450 million, 
although two hurricanes in the 1960's, Betsy (1965) and Camille 
(1969), each caused damage exceeding $1.4 billion. 26 Improved tech- 
niques in hurricane detection and warning have dramatically reduced 
the number of deaths caused by hurricanes ; however, property losses 
have continued to grow, as a result of increased population and activi- 
ties in vulnerable coastal areas, with the attendant concentration of 
new houses, buildings, and other facilities of higher replacement value. 
Figure 8 shows the simultaneous increase in property losses and de- 
crease in deaths due to hurricanes in the United States in the 20th 
century through 1969. 

Devastation and fatalities occur essentially from three phenomena 
associated with hurricanes : the force of the winds in the storm itself, 
the storm surge on coastal areas, and flooding which can result from 
excessive and widespread rainfall as the storm moves inland. Since 
wind force varies with the square of the wind speed, a 50-mile-per-hour 
wind exerts four times as much force as a 25-mile-per-hour wind. Ac- 
cordingly, a 10-percent reduction in maximum windspeed yields a de- 
crease in wind force of about 20 percent. 27 Attempts to modify hurri- 
cane winds can thus be expected to reduce storm damage caused by 
winds in approximate proportion to the corresponding reduction in 
wind force. 

25 Federal Coordinator for Meteorological Services and Supporting Research, U.S. Depart- 
ment of Commerce, National Oceanic and Atmospheric Administration, "National Hurricane 
Operations Plan," FCM 77- 2. Washington, D.C., May 1977, pp. 6-7. 

20 Gentry, K. Cecil, "Hurricane Modification." In Wilmot N. Hess (ed.). "Weather and 
Climate Modification," New York, John Wiley & Sons, 1974, p. 497. 

27 Ibid., p. 498. 


Figure 8. — Losses in the United States from hurricanes, 1915 through 1969, in 
5-year periods (from National Oceanic and Atmospheric Administration). 

_ As a hurricane moves across the coast from the sea. the strong winds 
pile up water to extreme heights, causing storm surges. The resulting 
onrushing water wreaks damage to shoreline and coastal structures. 
The severity of the storm surge is increased by the hurricane-generated 
wind waves which are superimposed on the surge. From Hurricane 
Camille, the storm surge at Pass Christian, Miss., was 24.6 feet, higher 
than any previous recorded tide. As a result, 135 people were killed, 
63,000 families suffered personal losses, and Mississippi alone sustained 
$1 billion in damage. 28 The height of the storm surge depends both on 

Anthes, Panofsky, Cahir, and Rango, "The Atmosphere," 1975, p. 159. 


the windspeed and the shape and slope of the sea bottom offshore. If 
there is a sharp dropoff in depth not far off the beach, the rise of the 
sea level will be small, for example. Nearshore attempts to modify a 
hurricane could lead to uncertain results, depending upon local condi- 
tions. If the windspeed is reduced without moving the position of 
maximum winds along the coast, the overall effect would likely be a 
reduction in storm surge. However, should the modification activity 
result in developing a new windspeed maximum at a different location, 
the surge might increase or decrease, depending on bathymetry and 
bottom topography. 29 Solutions are not yet clear, and the storm surge 
prediction problem is being studied intensely with the use of numerical 

Major hurricane damage can often be attributed to heavy rains and 
the massive and sudden flooding which can result as the storm move's 
inland. In mountainous regions especially, the floods from such rain- 
fall can be devastating in losses to both life and property. Such flood- 
ing was a major contributor to the 118 deaths and $3.5 billion in prop- 
erty destruction 30 which resulted in June 1972 from Hurricane Agnes, 
which set the record of achieving the greatest damage toll of all U.S. 
hurricanes. Ironically, Agnes caused almost no major damage as it 
went ashore. Hurricane modification activities which have been at- 
tempted or are contemplated are unfortunately not designed to reduce 
the rains significantly, but are intended rather to reduce the maxi- 
mum winds. 31 

Generation and characteristics of hurricanes 

A hurricane can be thought of as a simple heat engine driven by 
temperature differences between the center of the storm and its mar- 
gins. At each level the central column must be warmer than the 
surrounding area to insure maintenance of the strong convection on 
which the storm depends. 32 While the energy which forms extratropical 
cyclones is provided by temperature differences between different air 
masses, the energy which generates and maintains hurricanes and 
other tropical cyclones is derived from a single air mass through 
condensation of water vapor, and there are seldom present any of 
the frontal activities which are characteristic of storms originating 
in temperate latitudes. The moisture-laden winds continuously supply 
water vapor to the tropical storm, and the condensation of each gram 
of the vapor releases about 580 calories of latent heat. Within this 
thermally driven heat engine tremendous quantities of energy are 
converted from heat to mechanical motion in a short time, a fact 
readily apparent from the fury of the winds. The daily power of the 
energy liberated within a hurricane has been estimated to be about 
ten thousand times the daily power consumption in the United States. 33 
The importance of tin 1 ocean in providing moisture to a hurricane 
is seen in the weakening and dissipation of the storms after they have 
crossed coastlines and travel over land. 

20 Gentrv. "Hurricane Modification," 1974. p. 499. 

30 National Advisory Committee on Oceans and Atmosphere. "The Agnes Floods.: a Cost- 
Audit of the Effectiveness of t^c Storm and Flood Warning System of the National Oceanic 
and Atmosnheric Administration," a report for the Administrator of NOAA. Washington, 
D.C., Nov. 22. 1972. p. 1. 

:;1 Gentrv. "Hurricane-Modification." H>74. n. 490. 

^Donn. William L. "Meteorology." 4th edition. New York. McGraw-Hill, 1975, p. 336. 
"Ibid., p. 338. 


Exactly how hurricanes form is not yet fully understood. They 
are all generated in the doldrums (a region of equatorial calms), 
though rarely if ever within latitudes closer than 5 degrees from the 
Equator, over water whose temperature is at least 27° C. The relatively 
high surface temperature is necessary for initiation of the convection. 
Hurricanes are relatively rare features even of the tropics, and the 
exact triggering mechanism is not yet known. 34 Their origin is usually 
traced to a low pressure disturbance which originates on the equatorial 
side of the trough of an easterly wave. 

Such a tropical disturbance moves slowly westward and slightly 
poleward under the direction of the tropical east winds. If conditions 
are right, this cluster of thunderstorms intensifies as it reaches the 
region near the boundary between the tropical easterlies and the 
middle-latitude westerlies, at about 25° latitude. It may then follow 
a path which reverses toward the east as it leaves the tropics. The 
tracks of 13 major hurricanes in the Northwest Atlantic Ocean are 
shown in figure 9. 

The development of the intense storm which might result from the 
conditions noted above is described in the following way by Anthes 
et al. : 

The increased inflow toward the center of falling pressure produces increased 
lifting of air, so that the thunderstorms become more numerous and intense. The 
feedback cycle is now established. The inflowing air fuels more intense thunder- 
storm convection, which gradually warms and moistens the environment. The 
warmer air in the disturbance weighs less, and so the surface pressure continues 
to fall. The farther the pressure falls, the greater the inflow and the stronger 
the convection. The limit to this process would occur when the environment is 
completely saturated by cumulonimbus clouds. Further condensation heating 
would not result in additional warming, because the heat released would exactly 
compensate for the cooling due to the upward expansion of the rising air. 35 

34 Ibid. 

35 Anthes, Panofsky, Cahir, and Rango, "The Atmosphere," 1975, p. 154. 


Figure 9. — Tracks of thirteen major hurricanes in the Xorth Atlantic from 1879 
through 1955 (from U.S. Naval Oceanographic Office, Publication No. 21, 
Sailing Directions for the West Indies, 1958). 

As the storm forms, the winds begin to strengthen about the center, 
increasing especially to the right of the direction in which the center 
is moving, normally on the poleward side. The clouds organize them- 
selves into a system and dense cirrus move forward in the direction 
of the movement of the center. Suddenly, the pressure falls over a 
small area and hurricane force winds form a tight band of 20 to 40 


miles radius around the center. The well-organized clouds show a 
spiraling structure, and the storm acquires an eye, a small nearly 
circular area, coinciding with the region of lowest pressure. The winds 
in the eye are light and variable and the clouds are scattered or 
entirely absent. 36 As the storm matures, the pressure ceases to fall 
and the maximum winds do not increase further. Now the storm ex- 
pands horizontally and large amounts of air are drawn in. As the 
storm expands to a radius of about 200 miles or more it becomes less 
symmetrical. Figure 10 is a vertical cross-section of the structure of 
a typical mature hurricane, showing the direction of flow and cloud 
distribution. 37 

In spite of the great damage and fatalities caused by hurricanes, 
their effects are not completely destructive. In many areas of South- 
east Asia and the west coast of Mexico, tropical storms are depended 
upon for a large part of the water supply. Throughout the Southern 
United States, hurricanes have also provided valuable drought relief. 38 
- Hurricane and other tropical cyclones are always characterized by 
high wind velocities and by torrential rains. Wind velocities of 60 to 
70 knots and more are normal for such storms. The air rotates rapidly, 
moving spirally toward the center. Maximum gusts exceed 100 knots 
and may reach 200 knots, although such high speeds are unrecorded 
since instruments are blown away or made inoperable at these wind 
speeds. 39 

Figure 10. — Vertical cross section through a hurricane, showing typical cloud 
distribution and direction of flow, as functions of height and distance from 
the eye. (From Anthes, Panofsky, Cahir, and Rango, 1975.) 

Compared with extratropical storms, hurricanes are generally small, 
circularly shaped zones of intense low pressure, with very steep pres- 
sure gradients between the center and the periphery. The pressure 
drop between the eye and the periphery is quite large, 20 to 70 milli- 
bars being typical. The winds are in a constant circular cyclonic 
motion (counterclockwise in the Northern Hemisphere and clockwise 
in the Southern Hemisphere) ; however, the center of the storm is a 

36 p P tterssen. Sverre. "Introduction to Meteorology," second edition, New York, McGraw- 
Hill. 1958, pp. 242-243. 

37 Anthes. Panofsky. Cahir. and Rango. "The Atmosphere," 1975. p. 157. 

ssReihl, Herbert, "Introduction to the Atmosphere," New York, McGraw-Hill, 1965, pp. 

39 Gentilli. J.. "Tropical Cyclones." In Rhodes W. Fairbridge fed.). "The Encyclopedia 
of Atmospheric Sciences and Astrogeology." Reinhold, New York, 1967, p. 1028. 

* Widely scattered 
_ — — shallow cumulus 


Distance from hurricane center (km) 


calm region of low pressure, called the eye. which is about 10 miles 
across on the average. The warm dry character of this region is due 
to subsiding air, which is necessary for existence of the storm. Around 
the eye is the wall, consisting of cumulonimbus clouds and the at- 
tendant extreme instability and rising motion; in the wall area adja- 
cent to the eye, heavy rains fall. Out from the central zone altostratus 
and nimbostratus clouds mix to form a layer with a radius as great 
as 200 miles. At higher altitudes and reaching to the outer regions 
of the storm is a mixture of cirrus and cirrostratus clouds. 40 

In a mature hurricane a state of relative equilibrium is reached 
eventually, with a particular distribution of wind, temperature, and 
pressure. Such distributions for a typical hurricane are shown sche- 
matically in figure 11. Note that the greatest pressure change and the 
maximum windspeeds are in the region of the wall clouds, near the 
center of the storm. 41 

Figtjbe 11.— Radial profiles of temperature, pressure, and windspeed for a mature 
hurricane. The temperature profile applies to levels of 3 to 14 kilometers; 
pressure and windspeed profiles apply to levels near the surface. (From 
Gentry, 1974. ) 

Modification of hurricanes 

Since the damage inflicted by hurricanes is primarily a result of the 
high windspeeds, the principal goal of beneficial hurricane modifica- 

40 Jerome Williams. John J. Hipsinson. and John D. Rohrhoujjh. "Sea and Air: The 
Naval Environment," Annapolis. Md.. U.S. Naval Institute. 1968, pp. 262-263. 

41 Gentry. "Hurricane Modification." 1974. pp. 502-503. 


tion is the reduction of the severity of the storm's maximum winds. 
The winds result from the pressure distribution, which, in turn, is 
dependent on the temperature distribution. Thus, hurricane winds 
might be reduced through reduction of temperature contrasts between 
the core of the storm and the region outside. 

Gentry notes that there are at least two important fundamentals of 
hurricanes which have been established through recent studies, which 
suggest possible approaches to modification of the severity of the 
storms : 42 

The transfer of sensible and latent heat from the sea surface to the 
air inside the storm is necessary if the hurricane is to reach or retain 
even moderate intensity. 

The energy for the entire synoptic-scale hurricane is released by 
moist convection in highly organized convective-scale circulations lo- 
cated in and around the eye of the storm and in the major rain bands. 
The first principle accounts for the fact that hurricanes form only 
over warm tropical waters and begin to dissipate after moving over 
land or cool water, since neither can provide sufficient energy flow to 
the atmosphere to maintain the intensity of the storm. The second 
principle explains why such a low percentage of tropical disturbances 
grow to hurricane intensity. Possible field experiments for beneficial 
modification of hurricanes follow from these principles. On the basis 
of the first, techniques for inhibiting evaporation might be employed 
to reduce energy flux from the sea surface to the atmosphere. Based 
on the second principle, it might be possible to affect the rate of release 
of latent heat in that small portion of the total storm which is occupied 
by the active convective-scale motions in such a way that the storm is 
weakened through redistribution of heating. 43 

Gentry discusses a number of possible mechanisms which have been 
suggested for bringing about changes to the temperature field in a 
hurricane. 44 Since the warm core development is strongly influenced 
by the quantity of latent heat available for release in air columns ris- 
ing near the center of the storm, the temperature might be decreased 
through reducing the water vapor in these columns, the water vapor 
originating through evaporation from the sea surface inside the region 
of high storm winds. It has been suggested that a film spread over the 
ocean would thus reduce such evaporation. No such film is available, 
however, which could serve this purpose and withstand rupturing and 
disintegration by the winds and waves of the storm. Another sugges- 
tion, tiiat the cooling of the sea surface might be achieved through 
dropping cold material from ships or aircraft, is impractical, since 
such great expenditure of energy is required. It has also been postu- 
lated that the radiation mechanisms near the top of the hurricane might 
be modified through distribution of materials of various radiation 
properties at selected locations in the clouds, thus inducing changes to 
the temperatures in the upper part of the storm. This latter suggestion 
needs further evaluation both from the standpoint of its practicality 
and from the effect such a change, if included, would theoretically have 
on storm intensity. 

The potential schemes for hurricane modification which seem to be 
practical logistically and offer some hope for success involve attempts 

42 Ibid., 1974. p. 503. 
« Ibid., p. 504. 
44 Ibid., p. 505. 

34-857 O - 79 - 10 


to modify the mechanism by which the convective processes in the eye- 
wall and the rain bands distribute heat through the storm. Since water 
vapor is condensed and latent heat released in the convective clouds, it 
should be possible to influence the heat distribution in the storm 
through changing the pattern of these clouds. 45 Recent success in 
modifying cumulus clouds promises some hope of success in hurricane 
modification through cloud seeding. By modifying the clouds in a hur- 
ricane, the storm itself may be modified, since the storm's intensity will 
be affected through changing the interactions between the convective 
(cloud) scale and the synoptic (hurricane) scales. 46 Figure 12 shows 
how the properties of a hurricane might be redistributed as a result 
of changing the temperature structure through seeding the cumulus 
cloud structure outside the wall. The solid curves in the figure repre- 
sent distributions of temperature, pressure, and windspeed identical 
with those shown in figure 11 without seeding; the dashed curves rep- 
resent these properties as modified through seeding. 47 

The first attempt at hurricane modification was undertaken by sci- 
entists of the General Electric Co., on a hurricane east of Jacksonville, 
Fla., on October 13, 1947. Clouds outside of the wall were seeded with 
dry ice in order to cause freezing of supercooled water, so that the ac- 
companying release of latent heat might alter the storm in some man- 
ner. Results of the experiment could not be evaluated, however, owing 
to the lack of adequate measuring equipment for recording cloud char- 
acteristics. Furthermore, the penetration of the wall clouds to the eye 
or to the area of intense convection in the storm's rain bands was pre- 
vented by failure of navigation aids. Based on information acquired 
from more recent seeding experiments and increased understanding of 
hurricanes, it seems doubtful that the 1947 seeding could have been 
effective. 48 

« Ibid. 

"Ibid., p. 504. 
«Ibid., pp. 504-505. 
48 Ibid., pp. 505-506. 


Figure 12. — Radial profiles of temperature, pressure, and windspeed for a mature 
hurricane before (solid curves) and possible changes after (dashed curves) 
seeding. (The solid curves are the same as those in fig. 11.) (From Gentry, 

Hurricane seeding experiments were undertaken by the Department 
of Commerce and other agencies of the Federal Government in 1961, 
initiating what came to be called Project Stormfury. To date only four 
hurricanes have' actually been seeded under this project — all of them 
between 1961 and 1971 ; however, Stormfury has also included inves- 
tigation of fundamental properties of hurricanes and their possible 
modification through computer modeling studies, through careful 
measurements of hurricane properties with research probes, and 
through improvements in seeding capabilities. 

The goal of hurricane seeding is the reduction of the maximum winds 
through dispersing the energy normally concentrated in the relatively 
small band around the center of the storm. The basic rationale for seed- 
ing a hurricane with silver iodide is to release latent heat through 
seeding the clouds in the eye wall, thus attempting to change the tem- 
perature distribution and consequently weaken the sea level pressure 
gradient. It is assumed that the weakened pressure gradient will allow 
outward expansion, with the result that the belt of maximum winds 
will migrate away from the center of the storm and will therefore 
weaken. Actually, stimulation of condensation releases much more 
latent heat than 'first hypothesized in 1961, and theoretical hurricane 
models show that a new eve wall of greater diameter can be developed 
by encouraging growth of cumulus clouds through dynamic seeding. 49 

» Ibid., pp. 510-511. 


Following seeding of the four storms in Project Stormf ury, changes 
were perceived, but all such changes fell within the range of natural 
variability expected of hurricanes. In no case, however, did a seeded 
storm appear to increase in strength. Hurricane Debbie, seeded first 
on August 18, 1969, exhibited changes, however, which are rarely 
observed in unseeded storms. Maximum winds decreased by about 30 
percent, and radar showed that the eye wall had expanded to a larger 
diameter shortly after seeding. After Debbie had regained her strength 
on August 19, she was seeded again on August 20, following which 
her maximum winds decreased by about 15 percent. 50 Unfortunately, 
data are not adequate to determine conclusively that changes induced 
in Debbie resulted from seeding or from natural forces. Observations 
from Hurricane Debbie are partially supported by results from simu- 
lated experiments with a theoretical hurricane model ; however, simu- 
lation of modification experiments with other theoretical models have 
yielded contrary results. 51 

One of the problems in evaluating the results of hurricane modifi- 
cation is related to the low frequency of occurrence of hurricanes 
suitable for seeding experiments and the consequent small number of 
such experiments upon which conclusions can be based. This fact re- 
quires that hurricane seeding experiments must be even more carefully 
planned, and monitoring measurements must be very comprehensive, 
so that data acquired in the few relatively large and expensive experi- 
ments can be put to maximum use. Meanwhile theoretical models must 
be improved in order to show the sensitivity of hurricane characteris- 
tics to changes which might be induced through seeding experiments. 

Gentry has suggested that the following future activities should be 
conducted under Stormf ury : 52 

1. Increased efforts to improve theoretical models. 

2. Collection of data to further identify natural variability in 

3. Expanded research — both theoretical and experimental — on 
physics of hurricane clouds and interactions between the cloud 
and hurricane scales of motion. 

4. More field experiments on tropical cyclones at every oppor- 

5. Tests of other methods and material for seeding. 

6. Further evaluation of other hypotheses for modifying 

7. Development of the best procedures to maximize results of 
field experiments. 


The structure of tornadoes is similar to that of hurricanes, consist- 
ing of strong cyclonic winds 53 blowing around a very low pressure 
center. The size of a tornado, however, is much smaller than that of a 
hurricane, and its wind force is often greater. The diameter of a tor- 
so National Oceanic and Atmospheric Administration. "Stormfury— 1977 to Seed One 
Atlantic Hurricane U.S. Department of Commerce News, NOAA 77-248, Washington. 
D.C., Sept. 20. 1977, p. 3. 

51 Gentry, "Hurricane Modification," 1974. p. 517. 

^ Cyclonic > winds blow counterclockwise around a low pressure center in the Northern 
Hemisphere ; in the Southern Hemisphere they blow clockwise. 


nado is about one- fourth of a kilometer, and its maximum winds can 
exceed 250 knots in extreme cases. 54 On a local scale, the tornado is the 
most destructive of all atmospheric phenomena. They are extremely 
variable, and their short lifetime and small size make them nearly 
impossible to forecast with any precision. 

Tornadoes occur in various parts of the world; however, in the 
United States both the greatest number and the most severe tornadoes 
are produced. In 1976. there were reported 832 tornadoes in this coun- 
try, 55 where their origin can be traced to severe thunderstorms, formed 
when warm, moisture-laden air sweeping in from the Gulf of Mexico 
or the eastern Pacific strikes cooler air fronts over the land. Some of 
these thunderstorms are characterised by the Auolent updrafts and 
strong tangential winds which spawn tornadoes, although the details 
of tornado generation are still not fully understood. Tornadoes are 
most prevalent in the spring and occur over much of the Eastern two- 
thirds of the United States; the highest frequency and greatest devas- 
tation are experienced in the States of the middle South and middle 
West. Figure 13 shows the distribution of 71,206 tornadoes which 
touched the ground in the contiguous United States over a 40-year 

Even in regions of the world favorable to severe thunderstorms, the 
vast majority of such storms do not spawn tornadoes. Further- 
more, relatively few tornadoes are actually responsible for deaths and 
severe property damage. Between 1960 and 1970, 85 percent of tornado 
fatalities were caused by only 1 to iy 2 percent of reported tornadoes. 56 
Nevertheless, during the past 20 years an average of 113 persons have 
been killed annually by tornadoes in the United States, and the annual 
property damage from these storms has been about $75 million. 57 

Modification of tornadoes 

Alleviation from the devastations caused by tornadoes through 
weather modification techniques has been a matter of considerable 
interest. As with hurricanes, any such modification must be through 
some kind of triggering mechanism, since the amount of energy pres- 
ent in the thunderstorms which generate tornadoes is quite large. The 
rate of energy production in a severe thunderstorm is roughly equal to 
the total power-generating capacity in the United States in 1970. 58 
The triggering mechanism must be directed at modifying the circula- 
tion through injection of small quantities of energy. 

^ Anthes, Panofsky, Cahir, and Rango, "The Atmosphere," pp. 150, 180. 

50 NOAA news. "Skywarn 1977 — Defense Against Tornadoes," U.S. Department of Com- 
merce, National Oceanic and Atmospheric Administration. Rockville, Md., Feb. 18, 1977, 
vol. 2, No. 4, pp. 4-5. 

56 Davies-Jones, Robert and Edwin Kessler, "Tornadoes." In Wilmot N. Hess (ed.), 
"Weather and Climate Modification," New York, John Wiley & Sons, 1974, p. 552. 
» Ibid. 

58 Anthes, Panofsky, Cahir, and Rango, "The Atmosphere," 1975, p. 185. 


Figure 13. — Tornado distribution in the United States, where contours enclose 
areas receiving equal numbers of tornadoes over a 40-year period. Frequencies 
are based on number of 2-degree squares experiencing first point of contact 
with the ground for 71,206 tornadoes. (From Wilkins, 1967, in Encyclopedia 
of Atmospheric Sciences and Astrology, Reinhold.) 

Tornado modification has not been attempted in view of the pres- 
ent insufficient knowledge about their nature and the lack of adequate 
data on associated windspeeds. There are potential possibilities, how- 
ever, which can be considered for future research in tornado modifica- 
tion. One proposal is to trigger competing meteorological events at 
strategic locations in order to deprive a tornadic storm of needed in- 
flow. This technique, suggested by the presence of cumulus clouds over 
forest fires, volcanoes, and atomic bomb blasts could use arrays of 
large jet engines or oil burning devices. Another approach for dis- 
persal of convective clouds which give rise to thunderstorms might 
involve the use of downrush created by flying jet aircraft through 
the clouds. A further possibility would depend on changing the char- 
acteristics of the Earth's surface such as the albedo or the availability 
of water for evaporation. 59 

Tornadoes tend to weaken over rougher surfaces due to reduction 
of net low-level inflow. Upon meeting a cliff, tornadoes and water- 
spouts often retreat into the clouds, and buildings also tend to reduce 
ground level damage. Thus, forests or artificial mounds or ridges 
might offer some protection from tornadoes, although very severe 
tornadoes have even left swaths of uprooted trees behind. 60 

Modification of tornadoes by cloud seeding would likely bo the cheap- 
est and easiest method. Sodium iodide seeding could possibly shorten 
the life of a tornado if the storm's cold air outflow became stronger and 
overtook the vortex sooner, thus cutting off the inflow. Seeding a 
neighboring cell upstream of the low-level inflow might also be bene - 

09 Davies-Jones and Kessler, "Tornadoes," 1974, p. 590. 
» Ibid. 


ficial, if the rapidly developing seeded cloud, competing for warm, 
moist air, reduces the inflow and weakens the rotating updraft. It is 
also possible that seeding would increase low-level convergence, lead- 
ing to intensification of a tornado. 61 
Davies- Jones and Kessler conclude that : 

Any efforts to modify a severe storm with potential or actual tornadoes 
obviously will have to be carried out with extreme caution * * *. Actual modifica- 
tion attempts on menacing tornadoes are probably several years away. In the 
meantime, we should seek improved building codes and construction practices 
and continue research into the actual morphology of convective vortices. 62 

In spite of the speculations on how tornadoes might be modified, no 
tests have yet been conducted. The small size and brief lifetime of tor- 
nadoes make them difficult and expensive to investigate. However, in 
view of their destructiveness, they must be given more attention by 
meteorologists, who should seek ways to mitigate their effects. Only 
further research into the character of tornadoes, followed by careful 
investigation of means of suppressing them, can lead to this desired 
reduction in the effects of tornadoes. 

Technical Problem Areas in Planned Weather Modification 

In this section a number of major problem areas associated with the 
development of weather modification technology will be addressed. 
These topics are not necessarily confined to the modification of any one 
of the weather phenomena discussed in the previous section but apply 
in general to a number of these categories of phenomena. Some of the 
problem areas have implications which extend beyond the purely 
technical aspects of planned weather modification, bearing also on 
social, economic, and legal aspects as well. Included are discussions on 
the problems of seeding technology, evaluation of results of weather 
modification projects, extended area and extended time effects from 
advertent weather modification, and potential approaches to weather 
and climate modification which involve techniques other than seeding. 
The problems of inadvertent weather modification and of potential 
ecological effects from planned weather modification could also prop- 
erly be included in this section ; however, these topics are addressed in 
chapter 4 and 13, respectively, in view of their special significance. 

seeding techonology 

In recent years there has been progress in developing a variety of 
ice-nucleating agents available for cloud seeding, although silver iodide 
continues to be the principal material used. Other seeding agents which 
have been studied include lead iodide, metaldehyde, urea, and copper 
sulfide. Nucleants have been dispensed into the clouds from both 
ground-based generators or from aircraft. In some foreign countries, 
such as the Soviet. Union, rockets or artillery have been used to place 
the seeding material into selected regions of the clouds; however, this 
means of delivery does not seem to be acceptable in the United States. 

There have been both difficulties and conflicting claims regarding the 
targeting of seeding materials, particularly from groimd generators, 
ever since the earliest days of cloud seeding. It is always hoped that 

ft Ibid., pp. 590-591. 
«a Ibid., p. 591. 


the nucleant will be transported from the generator site by advection, 
convection, and diffusion to parts of the clouds which have been iden- 
tified for modification. Difficulties have been observed under unstable 
conditions, where the plume of nucleants was disrupted and wide angle 
turbulent diffusion was severe. Valley locations in mountainous areas 
are often subjected also to inversions and to local channeling so that 
trajectory determinations are extremely difficult. Even plumes of seed- 
ing material from aircraft have shown an erratic pattern. The prob- 
lems of irregular plume goemetry appear to increase as distortion 
occurs near fronts in mountain terrain, that is, under just the circum- 
stances where cloud seeding is often attempted. 63 

In view of the limited vertical transport of silver iodide observed 
in some studies (that is, up to 450 meters above the terrain at distances 
of several kilometers from the generators), some have concluded 
that, under conditions of the tests, ground-based generators are 
probably not effective. However, other studies have shown that one 
cannot generalize that ground generators are not always effective. 
Thus, more desirable effects can be achieved with generators at high 
altitudes where there is little chance of inversion trapping of the 
silver iodide as in other tests. 64 

Much of the ambiguity associated with ground-based generators is 
reduced when the nucleant material is placed into the cloud directly 
by an aircraft using flares or rockets. However, airborne seeding also 
presents important targeting problems. Of course, targeting difficul- 
ties are reduced in the case of single cloud seeding, where the aircraft 
is flying directly beneath the cloud in the active updraft area. How- 
ever, questions of proper vortical ascent persist when the objective is 
to lay down from the aircraft an elevated layer of nucleant-rich air 
that is intended to drift over the target area. 65 

In conclusion, the 1973 National Academy of Sciences study says : 

To summarize the results of the past few years' work on targeting, it can he said 
that earlier dobuts about the inevitability of nuclei reaching effective altitudes 
from ground generators tend to be supported by a number of recent observational 
studies. Some of these merely confirm the rather obvious prediction that stable 
lapse rates will be unfavorable to the efficacy of ground generators ; others indi- 
cate surprising lack of vertical ascent under conditions that one might have 
expected to favor substantial vertical transport. The recent work also tends to 
support the view that plumes from ground generators in mountainous terrain 
must be expected to exhibit exceedingly complex behavior ; and each site must 
be expected to have its own peculiarities with respect to plume transport. Tracking 
experiments become an almost indispensable feature of seeding trials or operations 
in such cases. 66 

There are three types of airborne seeding agent delivery systems in 
common use — burners, flares, and hoppers. Burners are used mainly 
for horizontal seeding, often at the cloud base as discussed above. Poly- 
technic flares are of two types — those used in vertical drops, similar to 
a shotgun shell or flare-pistol cartridge, and the end-burning type, 
similar to warning flares. The flares contain silver iodide with or with- 
out an auxiliary oxydizer, such as potassium nitrate, together with 
aluminum, magnesium, and synthetic resin binder. Dropping flares are 

68 National Academy of Sciences, National Research Council, Committee on Atmospheric 
Sciences, "Weather and Climate Modification : Problems and Progress," Washington, D.C.. 
1973. pp. 115-16. 

61 Ibid., p. 117. 

85 Ibid., pp. 118, 120. 

M Ibid., pp. 119-120. 


intended to be dropped into updrafts and to seed the cloud over a verti- 
cal depth as great as a kilometer, while burner seeding is intended to be 
more controlled and gradual. Hoppers dispense materials in solid form, 
such as the particles of dry ice crushed and dropped into clouds and 
cold fogs. For warm fog and cloud modification hoppers are used to 
dispense dry salt or urea. Sometimes these materials are pumped in a 
solution to nozzles in the wings, where the wingtip vortices help mix 
the agent into the air. 67 

On the ground there are a number of seeding modes which are fre- 
quently used, and types of nucleants used with ground-based genera- 
tors are commonly of two types — a complex of silver iodide and sodium 
iodide or of silver iodide and ammonium iodide. Outputs from the gen- 
erator are usually from 6 to 20 grams per hour, although generators 
with much greater outputs are used sometimes. One seeding mode in- 
volves dispensing continuously into the airstream from a ground gen- 
erator at a fixed point, the approach used most commonly in mountain- 
ous terrain. If the generator is located in flat country at temperatures 
above freezing, the nucleation level is reached through entrainment of 
the material into the convection. 68 

The nucleating effectiveness of silver iodide smoke is dependent upon 
the cloud temperature, where the colder the temperature the greater is 
the number of ice crystals formed per gram of silver iodide. Tests of 
nucleating effectiveness are made in the Colorado State University 
cloud simulation facility, where the nucleant is burned in a vertical 
wind tunnel and a sample of the aerosol is collected in a syringe and 
nucleant density calculated from the pyrotechnic burn rate and the 
tunnel flow rate. The syringe sample is diluted with clean, dry air and 
injected into a precooled isothermal cold chamber containing cloud 
droplets atomized from distilled water. Ice crystals which grow and 
settle out are collected on microscopic slides, so that nucleating effec- 
tiveness can be calculated as the ratio of concentrated crystals detected 
to the mass of nucleating material in the air sample. 69 

As part of the preparations for the 1976 seeding operations in the 
Florida area cumulus experiment (FACE) of the National Oceanic 
and Atmospheric Administration (NOAA), Sax et al., carefully 
evaluated the silver iodide effectiveness of different flares used in 
FACE. The results of these effectiveness studies, conducted with the 
Colorado State University facility, are shown in figure 14. It was dis- 
covered that a newly acquired airborne flare, denoted as NEI TB-1 
in the figure, was considerably more effective than both the Navy 
flares used earlier and another commercially available flare (Olin 
WM-105). The superiority of the NEI TB-1 material at warmer 
temperatures is particularly noteworthy. 70 In another paper, Sax, 
Thomas, and Bonebrake observe that crystalline ice concentrations in 
clouds seeded in FACE during 1976 with the NEI flares greatly 
exceeded those found in clouds seeded during 1975 with Navy flares. 

67 Ruskin, R. E. and W. D. Scott, "Weather Modification Instruments and Their Use." 
In Wilmot N. Hess (ed.), "Weather and Climate Modification," New York, Wiley, 1974, pp. 

68 Elliott, Robert D., "Experience of the Private Sector." In Wilmot N. Hess (ed.), 
"Weather and Climate Modification," New York, Wilev, 1974, p. 57. 

09 Sax, Robert I.. Dennis M. Garvey, Farn P. Parungo, and Tom W. Slusher, "Characteris- 
tics of the Agl Nucleant Used in NOAA's Florida Area Cumulus Experiment." In preprints 
of the "Sixth Conference on Planned and Inadvertent Weather Modification," Champaign, 
111., Oct. 10-13. 1977. American Meteorological Society, Boston, 1977, p. 198. 

70 Ibid., pp. 198-201. 


They conclude that, if differences in sampling time intervals and effects 
of instrumentation housing can be ignored, there is indicated a much 
greater nucleation effectiveness for the XEI flares which were used 
predominantly after July 1975. 71 The implications of this result are 
very far reaching, since the borderline and/or slightly negative results 
of many previous experiments and operational projects 1 can possibly 
be laid to the ineffectiveness of the silver iodide flares previously 

-5 -10 -15 -20 

Figure 14. — Effectiveness of various silver iodide flares in providing artificial 
nuclei as a function of cloud temperature. The principal comparison is between 
the XEI TB-1 and the Navy TB-1 flares (see text) ; the curve of mean data for 
the Olin WM-105 flares is included for comparison. The curves show that the 
XEI flares, used In FACE in late 1975 and 1976 were significantly more effec- 
tive in producing nuclei at warmer temperatures just below freezing. ( From 
Sax, Garvey, Parungo, and Slusher, 1977.) 


There has been much emphasis on evaluation methodology on the 
part of weather modification meteorologists and statisticians, partic- 
ularly with regard to precipitation modification. Progress in this 

71 Sax. Robert I.. Jack Thomas. Marilyn Bonebrake. "Differences in Evolution of Ice 
Within Seeded and Nonseeded Florida Cumuli as a Function of Nucleating Agent." In pre- 
prints of the "Sixth Conference on Planned and Inadvertent Weather Modification. " Cham- 
paign, 111., Oct. 10-13, 1977. Boston, American Meteorological Society, 1977," pp. 203-205. 


area has been slow, owing to the complexity of verification problems 
and to inadequate understanding of cloud physics and dynamics. 

Having reviewed previous considerations of evaluation attempts, 
Changnon discovered a wide variety of results and interpretations, 
noting that "a certain degree of this confusion has occurred because 
the methods being used were addressed to different purposes and 
audiences, and because there has been no widely accepted method of 
verification among investigators." 72 He continues : 

For instance, if one considers identification of changes in the precipitation 
processes most important to verification of modification efforts, then he will 
often undertake evaluation using a physical-dynamic meteorological approach. 
If he considers statistical proof of surface precipitation changes the best method, 
he may concentrate verification solely on a statistical approach or make in- 
adequate use of the physical modeling concepts. On the other hand, if the evalua- 
tion is to satisfy the public, the consumer, or the governmental decision-maker, 
it must be economic-oriented also. Hence, a review of the subject of previous 
evaluation methodology must be constantly viewed with these different goals 
and concepts in mind. 73 

Evaluation methodology for weather modification must deal with 
three fundamental problems which Changnon has identified : 74 

1. There are many degrees of interaction among atmospheric forces 
that result in enormous variability in natural precipitation, greatly 
restricting attempts for controlled experiments that are attainable 
in other physical and engineering sciences. 

2. There is an absolute need to evaluate weather modification with 
statistical procedures; this requirement- will exist until all underlying 
physical principles of weather modification can be explained. 

3. The data used in the evaluation must be sufficiently adequate in 
space and time over an experimental region to overcome and describe 
the natural variability factors, so that a significant statistical signal 
may be obtained within the noise of the variability. 

It is further recognized that analysis of weather modification ex- 
periments is closely akin to the weather prediction problem, since 
evaluation of weather modification efforts is dependent on a com- 
parison of a given weather parameter with an estimate of what would 
have happened to the parameter naturally. Thus, the better the pre- 
diction of natural events, the better can a weather modification proj- 
ect be designed and evaluated, at the same time reducing the verifica- 
tion time required by a purely statistical approach. 75 

Initially, weather modification evaluation techniques used only the 
observational or "look and see" approach, improved upon subsequently 
by the "percent of normal" approach, in which precipitation during 
seeding was compared with normals of the pre-experimental period. 
Later, using fixed target and control area data comparisons, regres- 
sion techniques were attempted, but the high variability of precipita- 
tion in time and space made such approaches inapplicable. In the 
mid-1960's there was a shift in sophisticated experiments toward 
use of randomization. In a randomized experiment, seeding events 
are selected according to some objective criteria, and the seeding 
agent is applied or withheld in sequential events or adjacent areas 

72 Changnon. Stanley A.. Jr.. "A Review of Methods to Evaluate Precipitation Modifica- 
tion in North America." Proceedings of the WMO/IAMAP Scientific Conference on Weather 
Modification. Tashkent. U.S.S.R.. Oct. 1-7, 1973, World Meteorological Organization. 
WMO— No. 399. Geneva, 1974, p. 397. 

73 Ibid., p. 398. 

74 Ibid. 

75 Ibid. 


in accordance with a random selection scheme. An inherent problem 
with randomization is the length of experimental time required; 
consequently, the approach is not often satisfying to those who wish 
to obtain maximum precipitation from all possible rain events or 
those who want to achieve results in what appears to be the most 
economical manner. As a result, commercial projects seldom make 
use of randomization for evaluation, and such techniques are gen- 
erally reserved for research experiments. 76 

In very recent years the randomization approach, which to many 
appeared to be too "statistical" and not sufficiently meteorological 
in character, has been improved on through a better understanding 
of atmospheric processes, so that a physical-statistical approach has 
been adopted. 77 

Changnon reviewed approximately 100 precipitation modification 
projects in North America and found essentiallv 6 basic methods 
that have been employed in project evaluations. He identified these 
as (1) direct observation (usually for single element seeding trials), 
(2) one-area continuous with no randomization (involving historical 
and/or spatial evaluation), (3) one-area randomization, (4) target- 
control area comparisons, (5) cross-over with randomization, and 
(6) miscellaneous. 78 These methods, along with the kinds of data 
which have been used with each, are listed in table 9. 



(From Changnon, "A Review of Methods to Evaluate Precipitation Modification in North America," 1974] 



precipitation data 

elements data 

economic data 

Direct observation Change in type; duration 

of precioitation; areal 
distribution (vs. model) 

One-area continu- Historical Area-rain regressions; 

ous (nonrandom). weekend-weekday 

rainfall differences; 
frequency of rain 

Spatial Area-rain regressions; 

pattern recognition; 
trend surfaces; rain 
rates; raindrop sizes; 
frequency of rain 
days; rain cell differ- 
ences; precipitation 
type change; areal 
extent of rain. 

Target control Area rainfall (day, 

month, season) repres- 
sions; area snowfall 
(day, month, season). 
One-area ran- Basically Area precipitation; 

domized (hours statistical. plume area precipi- 

pulsed). tation: change in pre- 

cipitation type. Period 
Physical plus precipitation; echo 
statistical. area; rain rates; echo 
reflectivity; rain 

Crossover ran- Area rainfall; zonal 

dnmized. rainfall. 

Miscellaneous (post 

hoc stratifica- 

Cloud parameters; echo 
parameters; seed and 

Frequency of severe Added runoff; crop 
weather; frequency yields; ecological, 
of smoke days. 

Synoptic weather con- Runoff increases; crop 
ditions; cloud parame- yields; ecological, 
ters; echo parameters; 
Agl plums; nuclei 
sources; airflow- 
plume behaviors; 
tracers in rain; atmos- 
pheric electrical 

Echo parameters Runoff regressions. 

Synoptic weather con- 
ditions; cloud parame- 
ters; seed material in 
plumes. Fcho parame- 
ters; Agl in rain; cloud 
numerical models; 
storm behavior; 
cloud base rain rate. 

Synoptic types and 
upper air conditions. 

Upper air: 

1. Temperature. 

2. Winds. 

3. Moisture stability 

Synoptic weather types. 

Water yield; runoff; 
ecosystem (plant and 
animals) and erosion; 
avalanche— disbene- 

76 Ibid., p. 399. 

77 Ibid., p. 400. 

78 Ibid., p. 407. 


The direct observation technique was the first major approach to 
evaluation and is still used occasionally. In addition to direct observa- 
tion of the change and type of precipitation at the surface, the time of 
precipitation initiation, and areal distribution following treatment of 
a cloud or cloud group, other meteorological elements have been ob- 
served ; these include radar echo characteristics, plume of the seeding 
material, and cloud parameters (microphysical properties and dynam- 
ical and dimensional properties such as updrafts, cloud size, and rate 
of growth.). 79 

The one-area continuous (nonrandomized) techniques have been 
employed to evaluate many of the commercially funded projects in 
North America, recent efforts to investigate inadvertent precipitation 
modification by large urban-industrial areas, and the statewide South 
Dakota seeding program. This category includes the largest number 
of projects, and control data for these nonrandomized projects have 
included both historical data and data from surrounding areas. The 
uncertainty of the control data as a predictor of target data is the basic 
problem in using this approach. 80 

* Most federally sponsored weather modification projects have used 
the one-area randomization method, which involves the use of a variety 
of precipitation elements, including duration, number of storms, and 
storm days and months. Projects evaluated with this method fall into 
two categories, including, as shown in table 9, those using the basic 
statistical approach and the more recent physical plus statistical tech- 
niques. The latter group of projects have been based on a greater 
knowledge of cloud and storm elements, using this information in 
defining seedable events and combining it with statistical tests to detect 
effects. Surface data, including rainfall rates and area mean rainfall 
differences, are used to evaluate such one-area randomized projects. 81 

The target-control method involves a single area that is seeded on 
a randomized basis and one or more nearby control areas that are never 
seeded and, presumably, are not affected by the seeding. 82 The method 
had been used in about 10 North American projects through 1974. 
Evaluation data have been mostly area rainfall or snowfall regres- 
sions, runoff differences, and radar echo parameter changes. 83 

The crossover (with randomization) method has been considered 
by many to be the most sophisticated of the statistical evaluation 
methods. The crossover design includes two areas, only one of which 
is seeded at a time, with the area for seeding selected randomly for 
each time period. As with the target-control method, a problem arises 
in this method in that there is the possibility of contamination of the 
control areas from the seeded area. 84 In the single project to which the 
method had been applied up to 1974, the evaluation procedure involved 
classification of potential treatment events according to meteorological 
conditions, followed by area and subarea rainfall comparisons. 85 The 

so Ibid., pp. 408-409. 

81 Ibid., p. 409. „ . „ T 

82 Brier. Glenn W. "Design and Evaluation of Weather Modification Experiments. In 
Wilroot N. Hess (editor), "Weather and Climate Modification," New York. Wiley, iy74. 

P ' safhangnon. "A Review of Methods To Evaluate Precipitaiton Modification in North 
America." 1974. p. 409. , . „' Wil 01A 

84 Brier. "Desiern and Evaluation of Weather Modification Experiments. 1974. p. 210. 

ssChangnon. "A Review of Methods To Evaluate Precipitation Modification in Nortn 
America," 1974, p. 409. 


miscellaneous methods in table 9 refer basically to evaluation efforts 
that have occurred after but generally within the context of the five 
methods mentioned above, and have been largely post-hoc stratifica- 
tions of results classified according to various meteorological subdivi- 
sions, followed by re-analysis of the surface rainfall data based on 
these stratifications. 86 

IFrom Changnon "A Review of Methods to Evaluate Precipitation Modification in North America," 1974] 


Surface hail data 

Meteorological elements Geophysical-economic 

Direct observation Cessation of hail; hail Echo parameters; cloud 

pattern; hail sizes parameters; Agl in hail. 

change; hailstone 


One-area continuous Historical Number of hail days 


Spatial Number of hail-produc- Radar echo character- 
ing clouds/unit time; istics. 
hailstreak frequencies; 
number of hail days; 
rainfall characteristics; 
impact energy; loca- 
tion of hail vs. total 
precipitation area. 

Target-control Energy; hail day frequen- Radar echo characteris- 

cy. tics. 

One-area random- Impact energy; hail day Radar echo characteris- 

ization. frequency; hailf all tics; Agl in hail-rain, 


Cross-over random- Energy; area of hail; vol- Agl in hail, 

ized. ume of hail. 

Crop-hail loss (insurance); 
insurance ratej. 
Crop-hail loss (insurance) 

Hail loss (insurance). 

Ecosystem (Agl); crop- 
loss data. 

About 20 projects concerned with hail modification were also ana- 
lyzed by Changnon with regard to the' evaluation techniques used. The 
five methods used, shown in table 10, include the first five methods 
listed in table 9 and discussed above for precipitation modification 
evaluation. A comparison of tables 9 and 10 reveals that the evaluation 
of rain and snow modification projects uses much less variety of kinds 
of data, especially the meteorological elements. The evaluation of hail 
projects is largely statistical, owing to the lack of sophistication in the 
physical modelling of hailstorms. There has been greater use of eco- 
nomic data in hail evaluation, however, than in evaluation of rainfall 
projects, due to some extent to the lack of surface hail data in weather 
records and the consequent need to make use of crop insurance data. 87 

In hail evaluation, the direct observation method has been used to 
look at physical effects from seeding individual storms and storm 
systems, involving analysis of time changes in surface hail parameters, 
radar echo characteristics, and cloud properties. The one-area contin- 
uous (non-random) method has been the principal one used in com- 
mercial hail projects and in studies of inadvertent urban-industrial 
effects on hail, using historical and/or spatial data in the evaluation. 
One major data form in these evaluations is the crop-hail loss from 
insurance data. The target-control method has made use of hail fall 
enerjry, hail-day frequencies, and crop-hail loss as evaluation data. 88 

» Ibid. 

87 IMd., pp. 412-413. 

88 Ibid., p. 413. 


The one-area randomization method is the method used in the Na- 
tional Hail Research Experiment. 89 Various degrees of randomization 
have been used, ranging from 50-50 to 80-20 ; however, the evaluation 
data have been similar to those used in other methods. Silver concen- 
trations in samples of rain and hail and elsewhere in the ecosystem 
have been used as evaluation criteria. The crossover randomized 
method of evaluation has also been applied to hail projects, using such 
data as areal comparisons of impact energy, area extent of hail, and 
total hail volume, noting also the concentrations of seeding material 
in the hailstones. 90 

A necessary part of any evaluation scheme involves the measurement 
or estimation of the amounts of precipitation fallen over a given area 
following seeded or control storm events. Such measurement is part of 
a more general requirement as well in collecting data for validation 
of weather predictions, development of prediction models, compilation 
of climatic records, and forecasting of streamrlow T and water resources. 
Although the customary approach to precipitation measurement has 
been to use an array of rain gages, weather radars have proven to be 
useful tools for studying generally the spatial structure of precipita- 
tion. Depending on the quality of the onsite radar system calibration, 
there have been varying degrees of success, however, in use of this 
tool. Often radar and rain gage data are combined in order to obtain 
the best estimate of precipitation over a given area. In this arrange- 
ment, the radar is used to specify the spatial distribution and the 
gauges are used to determine the magnitude of the precipitation. 91 
. Exclusive use of rain gauges in a target area in evaluation of con- 
nective precipitation modification projects requires a high gauge den- 
sity to insure adequate spatial resolution. For a large target area, such 
an array would be prohibitively expensive, however, so that weather 
radars are often used in such experiments. The radar echos, which 
provide estimates of precipitation, are calibrated against a relatively 
smaller number of rain gages, located judiciously in the target area 
to permit this calibration. 

It has been shown that adjusted radar estimates are sometimes 
superior to either the radar or the gages alone. Furthermore, the best 
areal estimates are obtained using a calibration factor which varies 
spatially over the precipitation field rather than a single average 
adjustment. Erroneous adjustment factors may be obtained, however, 
if precipitation in the vicinity of the calibration gage is so highly 
variable that the gage value does not represent the' precipitation 
being sampled by the radar. The technique for calculating the adjust- 
ment factor typically involves dividing the gage measurement by the 
summed rainfall estimates inferred from the radar, to obtain the 
ratio, G/E, used subsequently to adjust radar estimates over a greater 
area. 92 

89 The National Hail Research Experiment is discussed as part of the weather modifica- 
tion program of the Natonal Science Foundation, ch. 5, p. 274ff. 

90 Changnon, "A Review of Methods To Evaluate Precipitation Modification in North 
America," 1974, p. 413. 

91 Crane, Robert K., "Radar Calibration and Radar-rain Gauge Comparisons." In pre- 
prints of the "Sixth Conference on Planned and Inadvertent Weather Modification," Cham- 
paign, 111., Oct. 10-13, 1977. Boston, American Meteorological Society, 1977, p. 369. 

92 Klazura, Gerald E., "Changes in Gage/radar Ratios in High Rain Gradients by Varying 
the Location and Size of Radar Comparison Area." In preprints of the "Sixth Conference 
on Planned and Inadvertent Weather Modification," Champaign, 111., Oct. 10-13, 1977. 
Boston, American Meterological Society, 1977, p. 376. 


In the evaluation of hail suppression experiments, or measurements 
of hailfall in general, there must be some means of determining the 
extent and the magnitude of the hail. One technique is to use a net- 
work of surface instruments called hailpads. Since single storms can 
lay down hail swaths up to 100 kilometers long and tens of kilometers 
wide, made up of smaller patches called "hailstreaks," the spacings of 
hailpads must be reduced to a few hundred meters to collect quantita- 
tive data over small areas. Even over small distances of the order of 
1 kilometer, it has been discovered that total numbers of hailstones, 
hail mass, and hail kinetic energy can vary by over a factor of 10. 93 
Another means of estimating hailfall is through use of crop- damage 
studies. Such results are obtained through crop-loss insurance data, 
aerial photography of damaged fields, and combinations of these data 
with hailpad measurements. 94 


The term "extended area effects" refers to those unplanned changes 
to weather phenomena which occur outside a target area as a result of 
activities intended to modify the weather within the specified target 
area. Such effects have also been called by a variety of other names 
such as "downwind effects," "large-scale effects," "extra-area effects," 
"off-target effects," and "total-area effects." When the time dimen- 
sion is considered, those changes which occur, or are thought to have 
occurred, either within the spatial bounds of the target area or in 
the extended area after the intended effects of the seeding should 
have taken place are referred to as "extended time effects." These 
inadvertent consequences are usually attributed either to the transport 
of seeding material beyond the area intended to be seeded or the 
lingering of such material beyond the time during which it was to be 

In a number of experiments there have been indications that an 
extended area effect occurred. The present state of understanding does 
not permit an explanation of the nature of these effects nor have the 
experimental designs provided sufficient information to describe their 
extent adequately. The subject is in need of additional study, with 
experiments designed to provide more specific data over pertinent 
areal and time scales. In recent years two conferences on extended 
area effects of cloud seeding have been convened. The first conference, 
attended by 18 atmospheric scientists, was held in Santa Barbara, 
Calif., in 1971 and was organized by Prof. L. O. Grant of Colorado 
State University and by Kobert D. Elliott and Keith J. Brown of 
North American Weather Consultants. Attendees at the 1971 seminar 
discussed existing evidence of extended area effects, considered the 
possible means of examining detailed mechanisms responsible for 
the effects, and debated the implications for atmospheric water re- 
sources management. 

A second workshop was held, under the sponsorship of the National 

63 Morgan, Griffith M. and Nell G. Towery. "Surface Hall Studies for Weather Modifica- 
tion." In preprints of the "Sixth Conference on Planned and Inadvertent Weather Modi- 
fication," Champaign, 111., Oct. 10-13, 1977, p. 384. 

»* Ibid. 


Science Foundation, at Colorado State University, Fort Collins, Colo., 
Aug. 8-12, 1977. 95 The Fort Collins meeting was attended by 44 partici- 
pants, composed of social scientists, observationists, physical scientists, 
modellers, statisticians, and evaluators. The group was exposed to a 
mass of data from various weather modification projects from all over 
the world and proposed to accomplish the following objectives through 
presentations, workshop sessions, and general discussions : 

Renew the deliberations of the Santa Barbara seminar. 

Expand the scope of participation so as to integrate and inter- 
pret subsequent research. 

Better define the importance of extended spatial, temporal, and 
societal effects of weather modification. 

Prepare guidelines and priorities for future research direction. 96 
Extended area effects have special importance to the nontechnical 
aspects of weather modification. From deliberations at the 1977 
extended area effects workshop it was concluded that : 

The total-area of effect concept adds a new dimension to an already complex 
analysis of the potential benefits and disbenefits of weather modification. A speci- 
fied target area may have a commonality of interests such as a homogeneous crop 
in a farm area or a mountain watershed largely controlled by reservoirs built for 
irrigation and/or hydroelectric power generation. Socioeconomic analysis of this 
situation is much more direct than the consideration of the total-area of effect 
which may well extend into areas completely dissimilar in their need or desire for 
additional water. The spatial expansion of the area of effect may increase or de- 
crease the economic and societal justification for a weather modification program. 
The political and legal consideration may also be complicated by this expansion in 
scope since effects will frequently extend across state or national borders. 81 

The strongest evidence of extended area effects is provided by data 
from projects which involved the seeding of wintertime storm systems. 
Statistical analyses of precipitation measurements from these projects 
suggest an increase in precipitation during seeded events of 10 to 50 
percent over an area of several thousand square kilometers. Some of the 
evidence for these effects, based mostly on post hoc analyses of project 
data, appears fairly strong, though it remains somewhat suggestive and 
speculative in general. 98 

Based upon two general kinds of evidence: (1) observational evi- 
dence of a chemical or physical nature and (2) the results of large 
scale/long-term analyses ; a workshop group examining the extended 
area effects from winter orographic cloud-seeding projects assembled 
the information in table 11. It should be noted that the quality of the 
evidence, indicated in the last column of the table, varies from "well 
documented" and "good evidence" to "unknown" and "no documenta- 
tion available;" however, the general kinds of extended area and 
extended time effects from a number of winter projects are illustrated. 99 

95 Brown. Keith J., Robert D. Elliott, and Max Edelstein, "Transactions of Workshop on 
Extended Space and Time Effect of Weather Modification," Aug. 8-12, 1977, Fort Collins, 
Coio North American Weather Consultants, Goleta, Calif., February 1978. 279 pp. 

«* Ibid., pp. 7-9. 

67 Ibid., p. 13. 

68 Ibid., p. 10. 

"Warburton, Joseph A.. "Extended Area Effects From Winter-orographic Cloud Seeding 
Projects," report of workshop panel. In Keith J. Brown, et al. "Transactions of Workshop 
on Extended Space and Time Effects of Weather Modification," Aug. 8-12, 1977, Fort Col- 
lins, Colo. North American Weather Consultants, Goleta, Calif., February 1978, pp. 137-164. 



[From Warburton, 19781 




Type of effect of effect Area of effect Mechanism 

Quality of 

Ice crystal anvil production Spatial and 
from dry ice seeding of time, 
cumulus clouds, Blu3 
Mountains, Australia. 


Persistence of ice nuclei at 
Climax— probably Agl for 
days after seeding. 

Transport of Agl from Climax Spatial, 
generators to 30 km down- 

Silver in snow.Sierra Nevada do. 

and Rockies— up to 100 km 
from generators. 

Produced rain 
6-12 mm 
over 18-hour 

nuclei con- 

30 N/liter 
(-20° C). 

4 to 100X 

1500 km 2 Cirrus seeding Documentation 

and transport needed (is 

of crystals available), 
from seeding 
with C02. 

Unknown Unknown Well documented 

(is available). 

~40 km 2 Transport of Few aircraft 

nuclei. observations. 

Pressure reductions in seeded 
band periods, Santa Bar- 

Cirrus shield produced by 
airborne seeding, Warra- 
gamba, Australia. 

Time Max. —2 mb. 


Up to 25 per- 
cent of 
seeded days. 

Continuum from 

Continuum from 


sites < — 1000 

km 2 ). 
2000 km 2 (l 


Physical trans- 
port of Agl 
on hydro- 
meter's con- 
taining Agl. 
Dynamic heat 

Ice crystal 
seeding of 
lower clouds. 

5 yr of observa- 

Fair to moderate 

needed (is 


Projection description Type of effect 

Magnitude of effect Area of effect 

Quality of evidence 

Spatial 30 percent > 40- 

yr, average, 3 
successive yr. 

Time; long-term 10 to 40 percent. 

Spatial +25 percent. 

Victoria, Australia, drought 
relief— non-randomized. 

Warragamba and other large- 
scale experiments — Aus- 
tralia decrease in S/NS 
ratio wth years of experi- 
ment. 1 

Israel I— randomized north 
and central seeded. 

Santa Barbara band seed- do +25 percent (+50 

ing— randomized. percent in bands). 

Santa Barbara storm seeding do Unknown 

of multiple bands. 

Time Seed/no seed ratios 

of 1.5 to 4 mean 
50 percent-in- 

Spatial Unknown analysis 


35,000 km 2 ; conti- 
nuum from seed- 
ing sites. 

Artifact of analysis.. 

6,000 km 2 ; conti- 
nuum from seed- 
ing sites. 

3,000 km 2 ; conti- 
nuum from seed- 
ing sites. 


Santa Barbara duration of 
seeded/nonseeded bands. 

Climax and east to plains of 
Colorado using "homo- 
geneous" data base deter- 
mined by new synoptic 

3,000 km 2 ; conti- 
nuum from seed- 
ing sites. 

600 km*; 130 km 
east of Climax, 
30 to 50 km 
south of Denver. 

No documentation 

Reanalysis needed 
avoiding ratios 
and double ratios. 

Reliable records for 

Moderately well 


Good evidence. 


'Tasmania experiment may confirm artifact. 

Examination of data from summertime convective cloud-seeding 
projects reveals "more mixed"' results by comparison with data from 
wintertime projects, when extended area effects are considered. This 
general conclusion accords with the mixed results from evaluations 
of convective cloud seeding within the target area. It was concluded 
by participants on a panel at the 1977 Fort Collins workshop that, 
for summertime convective cloud seeding, there are statistical evi- 
dences of both increases and decreases in the extended area, though 
there are a large number of nonstatistically significant indications. 
Table 12 was assembled by the panel to summarize the characteristics 
of these effects for each of the projects examined. 1 

1 Smith. T. B.. "Report of Panel on Rummer Weather Mortification." In Keith J. Brown 
et al., "Transactions of Workshop on Extended Spare and Time Effects of Weather Modi- 
fication." Aug. 8-12. 1077. Eort Collins, Colo. North American Weather Consultants. Goleta. 
Calif.. February 1978. pp. 228-326. 




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It was the general consensus of the 1977 workshop participants 
that seeding can effect precipitation changes over relatively large 
areas which extend beyond the typical target area. Such changes can 
be positive or negative and may be of the same sign as the effect in 
the designated target area or of opposite sign. For example, among 
summertime projects considered the Israeli experiment provided sub- 
stantial evidence for positive effects in the target and in the extended 
areas (see table 12). Project Whitetop and the Arizona experiment, 
on the other hand, showed strong evidence of precipitation decreases 
in the target areas, downwind, and in surrounding areas. The Florida 
area cumulus experiment (FACE) revealed significant rainfall in- 
creases in the target area, but seemed to show decreases in surround- 
ing areas, and the 1969-1972 South Dakota project demonstrated 
negative seeding effects in the target area and positive effects in ex- 
tended areas. Of all projects reviewed, however, and in view of all the 
differing results suggested, the combination of target- and extended- 
area effects which appears to have the least support is that combina- 
tion most likely to occur to many lay people, i.e., increases in the tar- 
get area with compensating decreases in some area "downwind" — 
the "robbing Peter to pay Paul" analogy. 2 

Statistical evidence of extended area and time effects seems to be 
reasonably common; however, the mechanics causing these effects 
are not understood. It appears that there may be a number of mech- 
anisms which come into play, the dominating ones operating under 
various storm types and seeding techniques. In some projects there 
is evidence that seeding intensified the storm dynamically through 
release of latent heat of sublimation. In other cases silver iodide has 
been transported for distances of 100 kilometers downwind of the 
seeding area and has persisted for several days in the atmosphere 
after seeding. Also ice crystals produced from seeding may, in turn, 
seed lower clouds downwind. 3 

With particular regard to extended area or time effects in cumulus 
seeding experiments, Simpson and Dennis have identified the follow- 
ing list of possible causes : 

1. Physical transport of the seeding agent. 

2. Physical transport of ice crystals produced by a seeding agent. 

3. Changes in radiation and thermal balance, as for example, from 
cloud shadows or wetting of the ground. 

4. Evaporation of water produced. 

5. Changes in the air-earth boundary, such as vegetation changes 
over land or changes in the structure of the ocean boundary layer 
following cloud modification. 

6. Dynamic effects: 

(a) Intensified subsidence surrounding the seeded clouds, com- 
pensating for invigorated updrafts. 

(b) Advection or propagation of intensified cloud systems 
which subsequently interact with orography or natural 

(c) Cold thunderstorm downdrafts, either killing local convec- 
tion or sotting off new convection cells elsewhere. 

sp.rnwn. et nl., "Trnnsnotions of the Workshop on Extended Space and Time Effects of 
Weather Mortification." 1978, p. 11. 
' Ihid.. p. 12. 


(d) Extended space-time consequences of enhancement or sup- 
pression of severe weather owing to cumulus modification. 

(e) Alteration, via altered convection, of wind circulation pat- 
terns and/or their transports which could interact with other cir- 
culations, perhaps at great distances. 4 

Kecommended research activities to further explore and develop 
understanding of extended area and extended time effects of weather 
modification are summarized in the final section of this chapter, along 
with other research recommendations. 5 


Nearly all of the techniques discussed earlier for modifying the 
weather involve some kind of "cloud seeding." The exception is in the 
case of warm fog dispersal, where attempts to dissipate have also 
included mechanical mixing or application of heat. While most cloud- 
seeding techniques involve the use of artificial ice nuclei such as those 
provided by silver iodide particles, other "seeding" substances, such 
as dry ice, sodium chloride, urea, propane, and water spray, have been 
used in certain applications. Clouds have also been seeded with metal- 
ized plastic chaff in order to dissipate electrical charge build-up and 
reduce the incidence of lightning. 

There may also be some promise in future years of beneficially 
changing the weather, over both large and small scales of time and 
space, using technologies that are not in the general category of cloud 
seeding. Indeed, some such schemes have been proposed and there has 
been research conducted on a number of these possibilities. 

In the following chapter the effects of man's activities and. some nat- 
ural phenomena in changing the weather unintentionally will be dis- 
cussed. While these inadvertent effects may be of general concern and 
should be studied in view of potential dangers, they should also 
be understood inasmuch as they may provide valuable clues on how 
the atmosphere can be more efficiently modified for beneficial purposes. 
For example, major heat sources judiciously located might be used 
to affect weather in ways useful to man. 

Solution of problems which overlap considerations of both weather 
and energy could be investigated and solved in common by scientists 
and engineers working in both fields. Such research should be under- 
way and some practical applications could be forthcoming during 
the 1980's. Dissipation of supercooled clouds and fog over large and 
medium-sized cities, which now appears to be technically feasible, may 
become desirable when solar energy collectors are more common. Ee- 
duction of radiative losses to space could be facilitated by allowing 
the clouds to reform at night. It is speculated that this diurnal cycle 
of operation would tend to weaken inversions that are often associated 
with fog and low stratus and so tend to alleviate problems of air 
pollution, though there might be some increase of photochemical 
effects in the daytime with additional sunlight. 6 

Excess heat and moisture from nuclear and other powerplants and 
from their cooling towers could be usefully employed for generating 

4 Simpson and Dennis, "Cumulus Clouds and Their Modification," 19,74, pp. 274-277. 

5 See p. 143. 

6 Dennis and Gagln, "Recommendations for Future Research In Weather Modification," 
1977, p. 79. 


clouds if the plants are optimally located with regard to water sources 
and meteorological conditions. The clouds so formed might be used for 
protection to crops during periods of intense heat or as a shield over a 
city at night to prevent re-radiation of heat back to space. The clouds 
might also be seeded subsequently somewhere downwind of the power- 
plant to enhance precipitation. 

Recently, Simpson reviewed and summarized the state of research 
and development of a number of the nonseeding approaches to weather 
modification which have been proposed. 7 She discusses effects of 
changes to radiation and to sea-air interface processes : 

Some expensive, brute force successes have been obtained by burning fuels to 
clear fogs or even to create clouds. A more ingenious approach is to use solar heat 
to alter part of the air-surface boundary or a portion of the free atmosphere. 
Black and Tarmy (1963) proposed ten by ten kilometer asphalt ground coatings 
to create a "heat mountain"' to enhance rain, or to reduce pollution by breaking 
through an inversion. Recently Gray, et al. (1975) have suggested tapping solar 
energy with carbon dust over 100-1,000 times larger areas for numerous weather 
modification objectives ranging from rain enhancement to snow melt, cirrus pro- 
duction, and storm modification. The physical hypotheses have undergone pre- 
liminary modelling with promising results, while the logistics appear marginally 
feasible. Drawbacks are the unknown and uncontrollable transport of the dust 
and its environmental unattractiveness. 

A cleaner way of differentially heating the air appears to be a possible future 
byproduct of the space program. A Space Solar Power Laboratory is in the plan- 
ning stages at NASA. Its main purpose is to provide electric power, which will 
be sent by the space laboratory to the earth's surface. The microwave power 
will be converted to DC by means of groups of rectifying antennas, which dissi- 
pate a fraction of the power into heat. Preliminary calculations * * * indicate that 
the atmospheric effect of the estimated heating would be comparable to that by 
a suburban area and thus could impact mesoscale processes. Future systems 
could dissipate much more heat and could conceivably be a clean way to modify 
weather processes. It is not too soon to begin numerical simulation of atmospheric 
modifications that later generation systems of this type might be able to achieve. 

Radiation alteration appears to be a hopeful weather modification approach 
still lacking a developed technology. A cirrus cover has long been welcomed as 
natural frost protection when it restricts the nocturnal loss of long-wave radia- 
tion. More recently, the effect of cirrus in cutting off short-wave daytime radia- 
tion has been modelled and measured. * * * Artificial simulation of cirrus effects 
by minute plastic bubbles impregnated with substances to absorb selected wave- 
lengths received preliminary attention . . . but, to my knowledge has not been 

Alteration of the sea-air interface is also a potentially promising weather 
modification technique, particularly to suppress convection or to mitigate the de- 
struction by tropical hurricanes. However, the technology in this area may be 
farther from actual field trials than that in radiation. If methods could be de- 
veloped to restrict sea-air latent and sensible heat flux, the development from 
tropical storm to hurricane might be inhibited, while not losing rainfall or other 
benefits of the system. Presently the monomolecular films which cut down the 
evaporation from reservoirs do not stay intact in oceanic storm conditions, even 
if the logistics of their delivery over wide areas ahead of the storm were solved. 
Logistic obstacles have also impeded implementation of the promising idea of 
cooling the waters ahead of the hurricane by mixing up the ocean layer above the 
thermocline. 8 

One possible means of achieving the mixing of ocean layers to cool 
the sea surface, suggested above by Simpson, might be accomplished, 

7 Simpson. Joanne, "What Weather Modification Needs." 1977, unpublished, pp. 13--1.". 
(Most of the needs of weather modification identified In this unpublished paper, but not 
including her summary of nonseeding approaches, were published in another paper with 
the same title by Dr. Simpson : preprints of "Sixth Conference on Planned and Inadvertent 
Weather Modification." Champaign, 111., Oct. 10-13. 1977. Boston, American Meteorological 
Society. 1977, pp. 304-307. 

8 Ibid. 


at least in part, as a beneficial byproduct of another power source 
under development — the ocean thermal energy conversion (OTEC) 
concept. The OTEC plants, located in tropical waters where hurri- 
canes are spawned and grow, can provide surface cooling and so assist, 
at least in localized areas, in the abatement of tropical storms and their 
attendant damages. This is another area of overlap between energy 
and weather interests where cooperative research and development 
ought to be explored. 

Research Needs for the Development of Weather Modification 

In previous sections of this chapter the rationale and the status of 
development of the various techniques used to modify several kinds of 
weather phenomena were summarized and discussed in some detail. 
Applications of these techniques in both operational and research proj- 
ects were considered and some measures of the current effectiveness 
were presented. Among these discussions were a variety of statements, 
some explicit and some implied, on further research necessary to ad- 
vance weather modification technology. This section addresses re- 
search needs more generally and in a more sysf'matic manner. 
Included are specific requirements and recommendations identified by 
individual experts and organizations. Recommendations of a policy 
nature on weather modification research, such as the role of the Federal 
Government and the organizational structure for managing research, 
are discussed in chapter 6, which summarizes the recommendations of 
major policy studies. Current research programs of Federal agencies 
are discussed in some detail in chapter 5. 

Research recommendations summarized in this section are primarily 
concerned with advancing the technology of advertent weather modi- 
fication intended for beneficial purposes. Research needs in support 
of other aspects of planned weather modification and on inadvertent 
modification are included in other chapters on those subjects. In some 
cases, however, in the following sets of recommendations, research 
efforts in these other areas are included with those dealing with tech- 
nology improvement in order to preserve the completeness of the par- 
ticular set of recommendations. 

general considerations 

Peter Hobbs identifies four main phases through which most devel- 
oping technologies such as weather modification must pass — the estab- 
lishment of scientific feasibility, engineering development, demonstra- 
tion projects, and full-scale plant operation. 9 He illustrates these 
phases in terms of relative expenditures and elapsed time for each in 
figure 15 and discusses the probable stage of development for weather 
modification. Noting that some would optimistically place develop- 
ment of the technology as far along as the dashed line YY, he himself 
would more cautiously place the progress of weather modification in 
the vicinity of XX, so that the major task ahead remains as the testing 
of the scientific feasibility to produce significant artificial modification 
to the weather. 10 

9 Hobbs, Peter V., "Weather Modification ; a Brief Review of the Current Status and Sug- 
gestion for Future Research." Background paper prepared for the U.S. Department of Com- 
merce Weather Modification Advisory Board, March 1977, p. 10. 

10 Ibid. 


This scientific feasibility can best be shown, according to Hobbs, 
through "mounting comprehensive research programs to investigate 
the structure and natural processes which dominate a few relatively 
simple cloud and precipitation systems and to establish the extent and 
reliability with which they can be artificially modified." He cites as a 
principal reason for the lack of significant progress in recent years his 
contention that "most of the effort has been directed at attempts to 
modify very complicated storm systems about which little is known 
and good hypotheses for artificial modification are lacking." 11 


Figure 15. — Schematic of the relative costs and time associated with the four 
phases of development of a new technology. The vertical lines XX and YY 
indicate two widely differing views on the present stage of development of 
weather modification technology. (From Hobbs, 1977.) 

We have seen that there is some reason to accept weather modifica- 
tion techniques as having some degree of operational capability in 
possibly two areas — cold fog dispersal and snowfall enhancement from 
orographic clouds — though there is room for continued research and 
technique development in these as well as other areas of weather modi- 
fication. Although supercooled fogs accoimt for only 5 percent of all 
fog occurrences, their prevalence at airports in northeastern and 
northwestern North America makes cold fog dispersal a valuable tool. 
Seeding of wintertime orographic clouds in experiments and opera- 
tional projects in the western United States has probably resulted in 
snowfall increases of 10 to 30 percent under cert am conditions. 

Table 13 is a review and general outlook on weather modification, 
prepared by Ohangnon, showing the stage of development, possible 
economic value or years before operational usefulness, and status of 
research for 5 areas of weather modification, for the cold-tempera- 
ture and warm -temperature cases where applicable. The. table also 
shows Changnon's rough estimate of the complexity and difficulty in 

11 Ibid., pp. 10-12. 


relation to fog dispersal of the development of modification techniques 
for the other phenomena. 12 

Changnon emphasizes the fact that established techniques do not 
exist for significant modification of weather phenomena such as rain- 
fall and severe weather over the more populous and major agricul- 
tural areas of the eastern United States. He says that : 

If measurable economic gains are to be realized in the eastern two-thirds of 
the United States due to weather modification (largely rain "management", hail 
suppression, and abatement of severe winter storms), much more research and 
effort must be extended. This research will concern (1) the thorough study on 
a regional scale of the complex multicellular convective systems which are the 
major warm season rain and hail producers, and (2) the study of the cold season 
cyclonic systems. 13 

[From Changnon, "Present and Future of Weather Modification; Regional Issues," "75] 




Severe convective Cyclonic scale 
storms storms 

Cold temperatures Operational phase; 
«32°F). low cost; 


Operational phase Research phase; 
(+10 to +30 favorable on 

percent); low 
cost; research 

small clouds; 
questionable on 
large clouds 
and systems; 

Research phase; 
5 to 10 yrs 
before opera- 
tional; sub- 
stantial and 

Warm tempera- Research phase; 
tures (>32° F). 2 to 5 yrs: sub- 
stantial and 

Possible phase; Exploratory phase; 
little research. 1 modest 
research. 1 

Degree of 1.0. 
complexity (in 
relation to fog). 




Exploratory phase; 
more than 10 
yrs; research on 
tropical is 
modest; research 
on "other" 
storms is minor. 


Questionable economic value unless chain reaction is found. 

Hobbs discusses in detail some of the kinds of weather modification 
research projects which he feels would be fruitful : 

Some candidate projects for intensive investigation include the dispersal 
of cold and warm fogs, the enhancement of precipitation from isolated conti- 
nental-type cumulus clouds, and the targeting of winter orographic snowfalls. 
Our knowledge of each of these subjects has reached the stage where the mounting 
of comprehensive projects is likely to yield definitive results. Physical studies 
have demonstrated that cold fogs can be dissipated by seeding with dry ice, and 
this technique is now in use operationally at a number of airports ; however, a 
statistical study to quantify the reliability of this technique has not (to my 
knowledge) been carried out. It could provide the much needed "success story" 
for weather modification. The dispersal of warm fogs is a much more difficult 
problem which has not yielded to subtle approaches. The U.S. Air Force has 
concluded that the best approach to this problem is through direct heat input ; this 
approach appears sufficiently promising that it should be subjected to proper 
physical and statistical evaluation. The possibility of targeting winter orographic 
snowfall to specific areas on the ground (e.g., reservoirs) has been investigated. 
. . . The technique shows sufficient promise that further studies involving both 
physical and statistical evaluation should be carried out. Attempts at modifying 
the precipitation from cumulus clouds dates back to the beginning of modern 
weather modification (the 1940's) ; however, very few of these projects have 
involved both physical and statistical evaluation (and many have used neither). 

12 Changrnon, Stanley A., Jr., "Present and Future of Weather Modification; Regional 
Issues," 1975. pp. 172-174. 

13 Ibid., p. 172. 


In view of our growing understanding of the structure and life cycles of individual 
cumulus clouds, and the auvances which have been made in the numerical 
simulation of these processes, the time is now ripe to mount a substantial investi- 
gation to determine whether precipitation from these clouds can be increased. 

The primary components of the comprehensive research projects recommended 
above should be physical, statistical, and theoretical analysis. Physical evalua- 
tions should include comprehensive field studies using a wide range of airborne, 
ground, and remote probing techniques to evaluate the natural systems and the 
degrees to which they can oe artificially modified. Physical testing and evaluation 
of a proposed weather modification technique is best commenced prior to the 
establishment of a statistical design, for not only can physical evaluations check 
the feasibility of a proposed technique, but they can indicate the conditions under 
which it is most likely to be effective and thereby aid in sharpening or the 
statistical design. A sound weather modification technique should also be based 
on, or supported by, the best theoretical models available for describing the 
weather system under investigation. If the theoretical and physical studies 
indicate that a particular weather modification technique is effective, a carefully 
designed randomized statistical experiment should follow. Theoretical and 
physical evaluations should continue through the statistical experiment. An 
independent repetition of the experiment in at least one other geo raphieal 
area will generally be required. The confluence of results from theoretical, phys- 
ical, and statistical analyses carried out in two areas would permit sound 
quantitative evaluation of the effectiveness of an artificial modification 


In the 1973 study published by the National Academy of Sciences 15 
three broad research goals for weather modification were recommended 
along with specific research programs and projects required to achieve 
those goals. The three goals are : 

1. Identification by the year 1980 of the conditions under which 
precipitation can be increased, decreased, and redistributed in 
various climatological areas through the addition of artificial ice 
and condensation nuclei ; 

2. Development in the next decade of technology directed 
toward mitigating the effects of the following weather hazards : 
hurricanes, hailstorms, fogs, and lightning ; and 

3. Establishment of a coordinated national and international 
system for investigating the inadvertent effects of manmade pol- 
lutants, with a target date of 1980 for the determination of the 
extent, trend, and magnitude of the effect of various crucial pol- 
lutants on local weather conditions and on the climate of the 
world. 16 

Achievement of these national goals would require, according to 
the National Academy study, implementation of the following research 
efforts, some in support of all three goals and others as a means to 
achieving each of the three goals : 
A. Recommended research in support of all three goals : 

1. More adequate laboratory and experimental field programs 
are needed to study the microphysical processes associated with 
the development of clouds, precipitation, and thunderstorm 

14 Hohhs. "Weather Modification ;" a Brief Review of the Current Status and Suggestions 
for Future Research," 1977, pp. 12-13. 

1 5 Nnt'onal Academy of Sciences, "Weather and Climate Modification ; Problems and Prog- 
ress," 1973. 

" Ibid., p. 27. 


2. There is a need to develop numerical models to describe the 
behavior of layer clouds, synoptic storms, orographic clouds, and 
severe local clouds. 

3. There is a need for the standardization of instrumentation in 
seeding devices and the testing of new seeding agents. 

4. There should be established a number of weather modifica- 
tion statistical research groups associated with the major field 
groups concerned with weather modification and the inadvertent 
effects of pollutants. 

5. There should be created a repository for data on weather 
modification activities, and, at a reasonable price, such data should 
be made available for reanaiyses of these activities. 

B. Recommended research in support of goal 1 above : 

1. There is a continuing need for a comprehensive series of 
randomized experiments to determine the effects of both artificial 
and natural ice and cloud nuclei on precipitation in the principal 
meteorological regimes in the United States. 

2. Investigations into the feasibility of redistributing winter 
precipitation should be continued and expanded. 

3. Experiments need to be designed so that the effects of seeding 
on precipitation outside the primary area of interest can be 

4. Studies of the effects of artificial seeding on cumulus clouds 
and the numerical modeling of the seeding process should be con- 
tinued and expanded. 

C. Recommended research in support of goal 2 above : 

1. Investigations should be made to determine whether the seed- 
ing techniques presently used in the study of isolated cumlus 
clouds and in hurricane modification can be extended to, or new 
techniques developed for, the amelioration of severe thunder- 
storms, hailstorms, and even tornadoes. 

2. An expanded program is needed to provide continuous birth- 
to-death observations of hurricanes from above, around, within, 
and beneath seeded and nonseeded hurricanes and for testing of 
existing and new techniques for reducing hurricane intensities. 

3. Studies on the development of hurricane-modification tech- 
niques should include a randomization scheme in the design and 
conduct of experimental programs. 

4. A major national effort in fundamental research on hailstorms 
and hailstorm modification should be pursued aggressively. 

5. A comprehensive program dealing with research on warm 
fog and its dissipation should be undertaken. 

6. A high priority should be given to the development of a vari- 
ety of research techniques specifically designed for observing 
severe storms. 

D. Recommended research in support of goal 3 above : 

1. National and international programs should be developed 
for monitoring the gaseous and particulate content of the atmos- 
phere, with particular emphasis on modification by man's 

2. Satellite programs should be developed to monitor continu- 
ally, on a global basis, the cloud cover, albedo, and the heat bal- 
ance of the atmosphere. 


3. There should be enlarged programs to measure those para- 
meters that describe the climate of cities and adjoining country- 
sides and to determine the physical mechanisms responsible for 
these differences. 

4. Continued strong support should be provided to the major 
effort now underway, known as the Global Atmospheric Research 
Program, to develop properly parameterized mathematical models 
of the global atmosphere-ocean system, to obtain the observational 
data to test their efficacy, and to provide the computers that permit 
simulation of the effects of human activities on a worldwide scale. 17 

Some of the recommended research activities discussed above were 
already underway at the time of the 1973 National Academy study, 
but continuation or expansion of these efforts were advised. Since that 
time others have been initiated, and beneficial results from continua- 
tion and expansion of earlier efforts have been achieved. The overall 
decrease in funding of the Federal research program in the past few 
years has resulted in curtailments of valuable research projects identi- 
fied to meet the goals above, however, and the current level of research 
activities can hardly lead to achievement of the goals set by the Acad- 
emy study. The recent history of Federal funding for weather modi- 
fication is discussed and summarized in chapter 5, as part of the treat- 
ment on Federal activities. 18 


Concerned that its research programs be more responsible to societal 
needs, the Weather Modification Project Office of the National Oceanic 
and Atmospheric Administration (NOAA) established a small ad- 
vanced planning group in 1976. Consisting of one full-time and three 
part-time members, none of whom were permanent NOAA employees, 
the advanced planning group was charged with making recommenda- 
tions and preliminary plans for research projects to be carried out 
over the following 10 to 15 years. The group set about its task by 
visiting various user groups to learn opinions about past Federal 
research and by reviewing available literature and consulting scien- 
tists on past and current weather modification field programs. 19 

The advanced planning group acknowledged that considerable prog- 
ress had been made in weather modification in the past few years, 
but noted that the current research approach has the following short- 
comings : 

1. Research in the United States on stimulation of precipitation 
has been concentrated in the semiarid western States and in Flor- 
ida rather than in the Corn Belt, where the potential economic 
payoff is much greater. 

2. Research on stimulation of rainfall and on suppression of 
hail and lightning have been carried out in separate projects. A 
single project dedicated to the concept of precipitation manage- 
ment in large convective clouds would be more likely to solve the 
problem of changing hailfall and rainfall simultaneously to pro- 
duce net economic benefits. 

» Ibid., pp. 27-30. 

18 Sop n 242. 

w Dennis Arnott S. and A. Gaprln. "Rocommendat'ons for Future Research in Weather 
Modification," Weather Modification Program Office. Environmental Research T.aboartories, 
Nntionm Ocennic nnr] Atmospheric Administration, U.S. Department of Commerce, Bouldei* 
Colo., November 1977, 112 pp. 


3. Weather modification has usually been equated with cloud 
seeding. Other possible means of modifying the weather have 
been largely ignored. 

4. Weather modification is usually considered in isolation, 
rather than as an integral part of a total response to weather- 
related problems. There are exceptions : dry ice seeding to improve 
visibility during cold- fog episodes at airports is normally viewed 
as a supplement to, rather than a replacement for, good instru- 
ment landing systems. However, cloud seeding to increase pre- 
cipitation is sometimes viewed as an alternative to irrigation or 
water conservation measures, a situation we think is regrettable. 
Fortunately, research in inadvertent weather modification is tend- 
ing to break down the artificial isolation of research related to 
weather modification from other aspects of atmospheric science. 20 

Having examined the current weather modification research situa- 
tion as perceived by user groups and research scientists, the NOAA 
Advanced Planning Group proceeded to formulate recommendations 
for future research, using certain general technical, economic and soci- 
ological guidelines. Proposed research was evaluated on the basis of 
answers to the following questions : 

1. Will the project advance scientific understanding of atmos- 
pheric processes and thereby contribute to an improved capability 
to modify weather on a predictable basis ? 

2. Will the operational capability toward which the project is 
directed provide net economic benefit? 

3. Are the proposed research and the possible subsequent appli- 
cations socially acceptable % 21 

The group completed its study during 1977 and provided its recom- 
mended research program to NOAA's Weather Modification Project 
Office. The 5 specific recommendations are summarized below : 

1. Work should be continued to determine the potential for in- 
creasing rainfall from convective clouds in warm, humid air 
masses by seeding for dynamic effects. Design of a new, compre- 
hensive project to be conducted in the eastern half of the United 
States should begin immediately. This project should gather in- 
formation on the effects of seeding upon rainfall, hail, lightning, 
and thunderstorm winds both within and outside a fixed target 
area. Additional field studies in Florida to establish the physical 
mechanisms responsible for the apparent increases in total target 
rainfall during FACE 22 in 1975-76 should be performed during 
at least two seasons in parallel with the design of the new project. 
The results of the additional studies would be valuable input for 
the design of the new comprehensive experiment. 

2. Because of the promising beginnings of the Sierra Coopera- 
tive Project on orographic precipitation and the HIPLEX 23 work 
on cumulus clouds in the semiarid western States, and because the 
projects are likely to produce important results of wide applica- 

20 Ibid., p. 8. 
a Ibid., pp. 8-9. 

22 The Florida Area Cumulus Experiment (FACE), an experimental project sponsored by 
NOAA's discussed under activities of the U.S. Department of Commerce in ch. 5. p. 292. 

23 The Sierra Cooperative Project and the High Plains Cooperative Program (HIPLEX) 
are projects sponsored under the Division of Atmospheric Water Resources Management of 
the Bureau of Reclamation in the U.S. Department of the Interior. These projects are dis- 
cussed in ch. 5, pp. 258 and 263, respectively. 


tion, we see no reason for new initiatives in these areas until those 
projects are completed. 

3. In view of the need for more detailed knowledge of hurricane 
behavior, we recommend that research on hurricane modification 
be continued with the understanding that the research is a long- 
term effort with potenial payoff 10 to 20 years away. We recom- 
mend further that modeling and other theoretical work be intensi- 
fied to provide a better basis for interpretation of data from 
seeding trials. 

4. Concepts for hail suppression and lightning suppression 
should be subjected to fundamental reappraisal before the resump- 
tion of any field experiments. 

5. Long-range planning should be continued toward "futuristic" 
projects in which problems in deliberate, large-scale weather mod- 
ification, inadvertent weather modification, forecasting, and agri- 
cultural climatology would be treated together rather than 
separately. 24 


At the request of NOAA's Advanced Planning Group, whose study 
was discussed in the previous section, the North American Interstate 
Weather Modification Council (NAIWMC) 25 compiled information 
on recommended Federal weather modification research, based on the 
needs of users within NAIWMC member States. Opinions of State offi- 
cials on needed research were obtained from 16 States through meet- 
ings sponsored by California, North Dakota, Pennsylvania, South Da- 
kota. Texas, and Utah and through questionnaires sent out by the 
NAIWMC during 1976 and 1977. 

Table 14 summarizes results of the NAIWMC investigation, showing 
perceived needs for research for weather modification users, as inter- 
preted by the State officials. 26 Keyes notes that the major research area 
recommended by most State and local governments is in the evalua- 
tion of ongoing, long-term operational projects within those States. 
Other important research needs expressed were for further develop- 
ment of seeding technology and for economic, environmental, and 
societal studies necessary for eventual public acceptance of weather 
modification. 27 

15 The purposes, organization, and activities of the North American Interstate Weather 
Modification Council are discussed in some detail in ch. 7. p. 333. 

26 Reves. Conrad G.. Jr.. "Federal Research Needs and New Law Requirements in Weather 
Modification : the NAIWMC Viewpoint," testimony before the U.S. Department of Commerce 
We.ither Modification Advisory Board, Champaign, 111., Oct. 14. 1977. 

» Ibid. 



[From Keyes, 1977; table format from Dennis and Gagin, 1977] 

Major categories of research i 


Arizona a, b, c a, b, e... a, b, c 

California a, b, c a, b a, b, c 

Illinois a, b, c a, b, c, d. a, b, c Yes 

Indiana b, c a, b, c, e. b, c Yes 

Kansas a, b, c b, c a, c 

Maryland a, b, c b, c Yes Yes. 

Michigan a, b, c b, c a Yes 

Missouri a, b a, c 

North Carolina 2 

North Dakota a b, c, e c a. 

Pennsylvania c c Yes Yes 

South Dakota a, b, c b, c c 

Texas a, c a, b, d... c a, c. 

Utah a, b b, d a 

Vermont a a a a, c. 

Virginia s 

• Categories of Federal research: 

1. Evaluation: 

a. Of operational programs. 

b. Physical studies. 

c. Extra-area effects. 

2. Seeding technology: 

a. New seeding agents. 

b. Transport and diffusion, delivery methods. 

c. Hail suppression methods. 

d. New tools, for example, satellites. 

e. Public education. 

3. Economic, ecological, and societal studies: 

a. Economic benefits. 

b. Toxicity of agents. 

c. Societal studies. 

4. Detection of clandestine seeding. 

5. Inadvertent weather modification. 

6. Forecasting: 

a. Short range. 

b. Local topographic effects. 

c. Long range. 

3 Need a national policy first. 
3 Mainly hurricane modification. 



Recently, the chairman of the Committee on Weather Modifica- 
tion of the American Meteorological Society 28 summarized his com- 
mittee's recommendations on recommended weather modification re- 
search needs. 29 It was noted that the primary focus of such research 
should be in the areas of purposeful alteration of patterns of cloud 
systems and precipitation and in the inadvertent impact of man's 
activities. In view of critical water problems affecting large portions 
of the country and the potential for increased demand for application 
of weather modification techniques by water users, the necessity for 
improved understanding of underlying physical processes through 
pursuit of basic research was emphasized. In particular, the "real 
payoff" to improvements in purposeful weather modification should 
be seen as coming from increased ability to understand, predict, and 

28 Weather modification activities of the American Meteorological Society and purposes 
and concerns of its Committee on Weather Modification are discussed in ch. 8, p. 395. 

29 Silverman. Bernard A., testimonv before the U.S. Department of Commerce Weather 
Modification Advisory Board, Champaign, 111.. Oct. 14. 1977. 


control the formation and development of mesoscale 30 cloud systems. 31 

Subject areas for recommended research to accomplish basic under- 
standing of atmospheric processes necessary for the development of 
weather modification technology were presented by the AMS com- 
mittee in the following outline form : 32 

M esoscale Cloud Dynamics 

A. Effect of seeding on convective cloud development and 
evolution : 

1. Growth of convective clouds. 

2. Merger of clouds into groups and systems. 

3. Organization of inflow (coupling of midtroposphere with 
the boundary layer). 

4. Enhanced moisture budget efficiency. 

B. Interaction of clouds with each other and with their environ- 
ment : 

1. Response to mesoscale forcing function. 

2. Relationship between low-level convergence and cloud field 

3. Role of outdrafts in development and sustenance of cloud 

4. Role of anvils in the evolution of the cloud field. 

C. Precipitation "nowcasting" : 

1. Low-level convergence field as predictor of precipitation 

2. Kinematic and thermodynamic predictors and covariates for 
statistical evaluation. 

D. Need for a multidisciplined mesoscale experiment with strong 
physical emphasis. 

Precip itation Microp hysics 

A. Evolution of natural ice in cloud : 

1. Nucleation processes. 

2. Secondary ice production processes : 

(a) Laboratory studies of causality. 

(b) Field investigations to define' appropriate in-cloud 
criteria for multiplication of ice. 

B. Interaction between microphysics and dynamics to produce and 
sustain precipitation. 

C. Effect of seeding on (A) and (B) above. 

D. Distinction between microstructure of clouds developing over 
land and over water in terms of suitability for seeding. 

E. Clarification of microstructure of clouds developing within the 
hurricane environment in terms of suitability for seeding. 

F. Cloud microstructure climatology for selected regions of the 
United States. 

G. Effect of ice generation on charge separation and electrification 

30 Mpsosealo meteorological phenomena are those with horizontal dimensions ranging from 
a few tens of kilometers to a few hundred kilometers. 

a Silverman, testimony before Weather Modification Advisory Board, 1977. 
» Ibid. 


Area of Seeding Effect 

A. Induced by dynamic response of environment. 

B. Induced by diffusion of nucleating material : 

1. In orographic regions. 

2. Transport through convective processes. 

C. Insolation pattern resulting from mid- and upper-level outflow. 

Turbulence and Diffusion 

A. Targeting of surface-based source (s) of nuclei into desired cloud 

B. Entrainment processes related to cloud development. 

C. Spread of nuclei released in cloud (spatial and temporal 

Seeding Agents and Methods 

A. Nucleation efficiency studies. 

B. Particle sizing and composition analyses. 

C. Particle generation systems. 

D. Improvement of technology. 

Cloud Climatology for Technology Applicability 

A. National in scope. 

B. Frequency of occurrence of clouds by type. 

C. Cloud base and cloud top heights for selected regions. 

D. Properties of in-cloud microstructure. 

E. Aerosol characteristics. 

F. Radar population studies. 

G. Precipitation statistics. 

H. Model-derived "seedability" assessment. 

Inadvertent Impacts 

A. Effect on climatic change. 

B. Effect on air quality. 

,C. Effect on meteorology near large urban regions : 

1. Thermal pattern. 

2. Precipitation. 

3. Cloudiness. 

D. Effect on meteorology near deforested areas. 

Cloud M odeling 

A. Synthesis of numerical simulation with atmospheric observations 
on all scales. 

B. Inclusion of cloud interaction and outdraft convergence. 

C. Mesoscale forcing (e.g. sea breeze, topography, etc.). 

Improved Methods of Statistical Design and Evaluation 

A. Required to interpret results of new mesoscale experiment. 

B. Required for extraction of physical information from previously- 
performed nonrandomized experiments. 

34-857 O - 79 - 12 


Study of oak brush as elk forage — part of environmental research conducted 
part of Project Skywater. (Courtesy of the Bureau of Reclamation.) 




At the 1977 workshop on the extended area and extended time ef- 
fects of weather modification, participants developed some recommen- 
dations for future research into these effects. 33 The following research 
activities, not necessarily in any order of priority, were recommended 
to be undertaken immediately with current available tools or over a 
period of time, as appropriate : 

The use of computer simulation and modeling can provide 
important information on the areal coverage and magnitude of the 
effects of weather modification. It can also define the types of in- 
formation and the sensitivity required for future field 

Models developed to detect moisture depletion in natural and 
seeded cases as an airmass moves over successive mountain ridges 
should be applied and verified by field measurements in an area 
with a minimum of complexities caused by the introduction of new 
moisture sources. In situ measurements of temperature, pressure, 
liquid water content, ice crystal concentrations, and precipitation 
on the ground and in the air will be needed as inputs to the model 
and for model validation. 

An intensive study should be initiated on particulate transport, 
including the transport of both seeding material and ice crystals 
produced by seeding. Techniques are currently available to 
measure ice crystal concentrations, nuclei, and silver in precipi- 
tation. Special tracers are becoming available and should be de- 
veloped further. Eemote sensing techniques for measuring ice and 
water need further development. 

A re-analysis of some past field programs could be undertaken 
immediately. (The question of apparent decreases in seeding ef- 
fectiveness in successive years of the Australian experiment has 
not been resolved adequately as to whether this effect is real or an 
analysis artifact. The reported persistence of ice nuclei for days 
after seeding at Climax and its relationship to the apparent 
decrease in the seed/no seed ratios with time should be further 

Continuing monitoring should be initiated of such quantities 
as ice nuclei concentrations in project areas in order to establish 
new benchmarks. A modeling effort should also be undertaken to 
investigate the evaporation and reprecipitation processes. 

Studies of wide-area effects from seeding summer convective 
storm systems may require more preliminary work before mount- 
ing a major field effort since less is known about these phenomena. 
These studies should be directed toward acquiring information 
about the possible redistribution of convective instability and the 
microphysical effects including the transport of ice nuclei and/ or 
ice crystals, and the possible interactive effects when these par- 
ticles are entrained into other cloud systems. 

Prior to the design of a major wide-area study program, initial 
studies should include : cloud population studies, including time 

33 Brown, et al.. "Transactions of the Workshop on Extended Space and Time Effects of 
Weather Modification," 1978, pp. 14-18. 


and space distributions and cloud microphysics ; hypothesis de- 
velopment, including numerical modeling ; reexamination of pre- 
vious experimental programs ; augmentation of ongoing programs 
to study total-area effects; and development of new capabilities 
including satellite measurements, rain gage network design, data 
processing, and management and seeding delivery systems. 

The final design of a field program will be dependent on the 
findings from these preliminary studies. It appears likely that it 
will be necessary to mount a major effort to determine the total- 
area effects and mechanics of convective storm seeding. Prelimi- 
nary estimates call for a 10-year studv covering nn area of at least 
a 300-mile radius in the mid-United States. Ideally this study 
could be operated in conjunction with other mesoscale field studies 
in cumulus convection and precipitation forecasting. 

A national technology assessment on precipitation modification 
should be conducted with the total-area effect included in both 
the physical science and social science context. 34 

a* Ibid. 



(By John R. Justus, Analyst in Earth Science, Science Policy Research Division, 
Congressional Research Service) 

Out of the total ensemble of environmental factors, the subset which 
is sensed most immediately and directly by man and which has the 
greatest integrated impact on human activities is that which is sub- 
sumed under the terms of iveather and climate. — Earl W. Barrett, 
1975, National Oceanic and Atmospheric Administration. 


The relationship between man and weather has been basically the 
one stated succinctly by Charles Dudley Warner: Everybody talked 
about the weather, but nobody did anything about it. In the 1940's, 
however, the discovery that clouds could be modified by additions of 
freezing nuclei created a realization that, at some times and places at 
least, it might be possible to do something about the weather. This 
entering wedge into the field of intentional or planned weather modi- 
fication has since been heavily studied and exploited ; it had, as a by- 
product, the creation of considerable interest in weather modification 
on the part of both the scientific community and the general popula- 
tion. The science and technology of planned weather modification are' 
discussed in chapter 3. The possibility that man has, in fact, been doing 
something about the weather without knowing it has become a subject 
for serious consideration, and chapter 4 reviews a number of processes 
and mechanisms governing inadvertent weather and climate modifi- 


By way of clarification, it is important to appreciate the fact that 
differences of scale are implied in the terms "weather modification" 
and "climate modification." 


To most everyone, the term climate usually brings to mind an aver- 
age regime of weather or the average temperature and precipitation 
of a locality. This is a rather misleading concept, for the average may 
be a rare event. Actually, weather from year to year oscillates widely 
so that climate is a statistical complex of many values and variables, 
including the temperature of the air, water, ice, and land surfaces; 
winds and ocean currents ; the air's moisture or humidity ; the cloudi- 
ness and cloud water content, groundwater, lake levels, and the water 
content of snow and of land and sea ice; the pressure and density of 



the atmosphere and ocean; the composition of (dry) air; and the 
salinity of the ocean. All of these elements encompass climate and are 
interconnected by the various physical and dynamic processes occur- 
ring in the system, such as precipitation and evaporation, radiation, 
and the transfer of heat and momentum by advection (predominantly 
horizontal, large-scale motions of the atmosphere), convection (large- 
scale vertical motions of the atmosphere characterized by rising and 
sinking air movements), and turbulence (a state of atmospheric flow 
typified by irregular, random air movements) . 

Climatic fluctuation and climatic change 

Rather than by average value, these elements are best characterized 
by frequency distributions, which can, in many places, span a wide 
range for a given element. Within such a range, one notes irregular 
fluctuations characterized by the occurrence of extreme values for given 
elements of the climatic system. In such instances, a climatic fluctua- 
tion is said to be experienced, not a climatic change. A change denotes 
that a new equilibrium had been achieved, and with it, a rather dif- 
ferent frequency distribution for all climatic elements. Thus, the term 
change is not to be confused with fluctuation, where trends are fre- 
quently reversed, even though some successive values may cluster for 
a while on one side or the other of the "average." 


Defined as the state of the atmosphere at any given time, the prev- 
alent belief of the public, that wherever the weather goes the climate 
follows, is fallacious. On the contrary, wherever the climate goes, so 
goes the weather. Weather is merely a statistic of the physical climatic 

Weather modification 

As used in the context of this chapter and in the text at large, 
weather modification refers collectively to any number of activities 
conducted to intentionally or inadvertently modify, through artificial 
means, the elements of weather and, in turn, the occurrence and be- 
havior of discrete weather events. Intentional or planned weather 
modification activities may be conducted for a variety of different 
purposes, including: Increasing or decreasing rain and snow over a 
particular area; reducing damage to crops and property from hail; 
reducing the number of forest fires that are started by lightning; 
removing fog at airports; changing the intensity and direction of 
hurricanes so they cause less destruction ; mitigating the destructive- 
ness of severe thunderstorms and tornadoes. 

Climate modification 

This encompasses the planned or inadvertent alteration, through 
artificial means, of the elemental properties comprising the air, sea, ice, 
land, and biospheric components of the climatic system in order to 
effect a new equilibrium among the elements of climate and, conse- 
quently, a new climate regime. In most instances, the term alludes to 
mesoscale and macroscale climates, from those of regions to the entire 
globe. Another common usage is in reference to the microscale climates 
of cities where persistent, inadvertent effects on weather, in turn, 
modify the climates of greater metropolitan areas. 


Planned climate modification 

While the term climate usually brings to mind an "average" regime 
of weather or, more properly, a frequency distribution of the elements 
and events of weather, the climatic system itself consists of those 
elements and processes that are basically the same as those responsible 
for short-term weather and coordinately for the maintenance of the 
long-term physical climatic state. It follows, then, that one of the pur- 
poses of planned weather modification activities may be to artificially 
change the climate of a location or region through means including, 
but not necessarily limited to: Massive and protracted extension of 
present cloud-seeding operations to influence natural precipitation de- 
velopment cycles; intentional initiation of large heat sources to influ- 
ence convective circulation or evaporate fog ; intentional modification 
of solar radiation exchange or heat balance of the Earth or clouds 
through the release of gases, dusts, liquids, or aerosols in the atmos- 
phere; planned modification of the energy transfer characteristics of 
the Earth's land or water surface by dusting with powders, liquid 
sprays or dyes, water impoundment, deforestation, etc. 

The dramatic idea of some great technological leap toward purpose- 
fully altering climate never seems to lose its appeal. The problem with 
these grand schemes is that, even if feasible, every fix — technological 
or otherwise — has its toll in side effects. But leaving aside for the 
moment the question of whether it makes sense to alter or conserve 
climate, many of the schemes that have been suggested for modifying 
climate on a hemispheric or global scale have so far been considered to 
be on the fringe of science fiction. The range of possibilities widens 
rapidly if one imagines the financial resources of the major world 
powers available to carry them out. Periodically resurgent are such 
schemes as darkening, heating, and melting of the Arctic icepack, the 
damming of the Bering Strait, the transportation of Antarctic ice- 
bergs, the diverting southward of North American and Asian rivers 
that empty into the Arctic, and the modification of tropical storms. 1 
These and other perennial suggestions are summarized in Figure 1. 

iKellogjr. W. W. and S. H. Schneider, "Climate Stabilization: For Better or for Worse?" 
Science, vol. 186, Dec. 27, 1974, pp. 1163-1172. 


Figube 1. — A survey of grandiose schemes that have been proposed to modify or 
control climate. (From Kellogg and Schneider, 1974.) 

Inadvertent climate modification 

The modification processes may also be initiated or triggered in- 
advertently rather than purposefully, and the possibility exists that so- 
ciety may be changing the climate through its own actions by pushing 
on certain leverage points. Inadvertently, we are already causing 
measurable variations on the local scale. Artificial climatic effects have 
been observed and documented on local and regional scales, partic- 
ularly in and downwind of heavily populated industrial areas where 
waste heat, particulate pollution and altered ground surface char- 
acteristics are primarily responsible for the perceived climate modifi- 
cation. The climate in and near large cities, for example, is warmer, 
the daily range of temperature is less, and annual precipitation is 
greater than if the cities had never been built. The climate of the world 
is governed mainly by the globally averaged effects of the Sun, the 
location and movement of air masses, and the circulation patterns of 
the world ocean. It is by no means clear that the interaction of these 
vast forces can be significantly influenced by human activities. Al- 
though not verifiable at present, the time may not be far off when 
human activities will result in measurable large-scale changes in 
weather and climate of more than passing significance. It is important 
to appreciate the fact that the role of man at this global level is still 
controversial, and existing models of the general circulation are not yet 
capable of testing the effects in a conclusive manner. 

Nevertheless, a growing fraction of current evidence does point to 
the possibility of unprecedented impact on the global climate by 
human activities, albeit the effects may be occurring below the thres- 
hold where they could be statistically detected relative to the record 


of natural fluctuations and, therefore, could be almost imperceptible 
amid the ubiquitous variability of climate. But while the degree of in- 
fluence on world climate may as yet be too small to detect against the 
background of natural variations and although mathematical models 
of climatic change are still imperfect, significant global effects in the 
future are inferred if the rates of growtn of industry and population 

historical perspective 

The possibility of climatic alterations by human activity was alluded 
to in the scientific literature at the beginning of this century, and again 
in the late 1930's, but it received little serious attention until the 1950 s. 
The first period of thermonuclear testing, 1954 to 1958, generated a 
great deal of concern about drastic and widespread elfects on weather. 
It was felt that anything which liberated such great energies must 
somehow influence the atmosphere. The fact that a device fired at sea 
level or under the sea did create locally a large convective cloud was 
cited as evidence. 

By about 1960 work had shown that no large-scale or long-term 
meteorological effects would ensue from nuclear testing at the levels 
conducted in the 1950 ? s. It had become clear that the inertia of the 
atmosphere-ocean system was too large to be perturbed seriously by the 
sudden release of any energy man could generate. Instead of the spec- 
tacular and violent, it was realized that one would have to look to the 
slow and insidious to find evidence of human influences on climate and 

Some evidence that manmade carbon dioxide was accumulating in 
the atmosphere appeared as early as 1938. This, together with some 
early systematic data from Scandinavia, led to the inclusion of a car- 
bon dioxide (C0 2 ) measurement program during the International 
Geophysical Year (IGY), 1957-1958. This C0 2 measurement pro- 
gram, which continues today, was the first serious scientific study of 
a possible manmade climatic influence on a large scale. 

As the reality of the C0 2 effect became established, and as the gen- 
eral mood of increased concern for the environment and the concept 
of "spaceship Earth" developed during the 1960's, increased scientific 
efforts began to be focused on inadvertent weather and climate modi- 
fication. It had been recognized for some time that the climates of 
cities differed significantly from their rural environs due to the re- 
lease of heat and pollutants. It was not until the late 1960's that evi- 
dence of "urban effect" on the climate at considerable distances down- 
wind began to be noticed. The role of pollution aerosols 2 as climate 
modifiers became a topic of great interest, and it remains so today. 

In the United States, the attention of the Government to these 
problems began with the IGY effort, C0 2 and solar radiation measure- 
ment programs were started in Antarctica and at the Mauna Loa Ob- 
servatory in Hawaii, which was established specifically for this pro- 
gram by the U.S. Weather Bureau. This station, located at an eleva- 
tion of 3,400 meters (11,155 feet) on the north slope of Mauna Loa, 

2 Dispersions in t b e atmosphere of particles of matter that remain suspended for a sig- 
nificant length of time. 


has been improved over the years and remains the prototype "bench- 
mark" station for climatic change monitoring. 

The first major meeting devoted exclusively to the inadvertent 
modification problem convened in Dallas, Tex., in December 1968. 3 

The following year, a series of discussions between some faculty 
members of the Massachusetts Institute of Technology, government 
officials and scientists gave rise to the first working conference, the 
Study of Critical Environmental Problems (SCEP). This meeting, 
held at Williams College, Wihiamstown, Mass., during July 1970, was 
devoted to identifying possible global environmental hazards and 
making recommendations concerning monitoring, abatement, et cetera. 
The climatic problem areas identified were carbon dioxide and other 
trace gases that may affect climate ; particulate matter in the atmos- 
phere as turbidity and as cloud modifiers ; waste heat ; changes in the 
Earth's surface (land-use changes) ; radioactivity in the atmosphere; 
and jet aircraft pollution of the high troposphere and stratosphere. 
The proceedings of this meeting were published by the MIT Press. 4 ' 5 

The working group for SCEP was, with one exception, composed of 
residents of the United States : scientists, representatives of industrial 
management, and government officials. Some of the participants felt 
that a more multinational participation would be essential if standard- 
ized global programs were to come into existence as a result of such 
a meeting. Also, it was the opinion that the problems of climate modi- 
fication were complex enough to occupy the entire attention of a work- 
ing meeting. As a result, a second such meeting was held, this time in 
Stockholm, with scientists from 14 countries participating. This work- 
ing meeting was called Study of Man's Impact on Climate 1 (SMIC). 
The report prepared by this group 6 dealt with the substantive scien- 
tific questions of inadvertent climate modification, including: previous 
climatic changes; man's activities influencing climate; theory and 
models of climatic change; climatic effects of manmade surface 
ciianges; modification of the troposphere; 7 and modification of the 
stratosphere. 8 One objective of SMIC was to provide guidelines for 
the World Meteorological Organization (WMO) and other interna- 
tional agencies to use in establishing monitoring and research pro- 
grams on a global scale. 

In connection with the study of inadvertent climate modification, 
much was iterated in the early 1970's about the need for global moni- 
toring. Because of the lagtime in planning, financing, and construct- 
ing such facilities (which must necessarily be in wilderness areas in 
order to give representative data not reflecting local effects), the 
minimum number of benchmark stations (10) considered necessary 
has not yet been reached. Five stations are currently in operation. 
Mauna Loa Observatory (MLO), the oldest, was established by the 

3 Singer, S. F., "Global Effects of Environmental Pollution," New York. Springer-Verlag, 

^Wilson Carroll L , editor. Man's Imnact on the Global Environment, Report of the 
Study of Critical Environmental Problems (SCEP). Cambridge, MIT Press, 1970, 319 pp. 

G Matthews, W. H., W. W. Kellogg, and G. D. Robinson, editors. "Man's Impact on the 
Climate." Cambridge, MIT Tress. 1971, r>*)4 pp- 

"Wilson C L and W IT Matthews, editors, Inadvertent Climate Modification, Report 
of the Study of Man's Impact on Climate (SMIC). Cambridge, the MIT Press, 1971, 30S pp. 

7 Troposphere — the inner layer of the atmosphere varying in height from to 12 miles. 
This is the region within wMch nearlv all weather conditions manifest themselves. 

8 Stratosphere — the region of the atmosphere outside the troposphere, about 10 to 30 
miles in height. 


U.S. Weather Bureau, then transferred to the supervision of the 
Atmospheric Physics and Chemistry .Laboratory of the Environ- 
mental Science Services Administration in I96ii and finally to the Air 
Resources Laboratory of the National Oceanic and Atmospheric Ad- 
ministration (NOAA) in 1971. In the following year, the NOAA net- 
work was officially expanded to four stations: MLO; South Pole; 
Point Barrow, Alaska ; and American Samoa. The other operational 
station is located at Kislovodsk, North Caucasus, in tne U.S.S.E. The 
Government of Canada has plans for three high latitude northern 
stations, and some limited monitoring activities are conducted in Aus- 
tralia and New Zealand. 

In addition to the long-term monitoring program, two shorter 
programs have been devoted to the inadvertent modification problem. 
The first of these, the Metropolitan Meteorological Experiment 
(Metromex), was directed toward a concentrated investigation of 
downwind eiiects of the thermal and particulate emissions from a typi- 
cal metropolitan area — St. Louis, Mo. The project involved an exam- 
ination of all available climatological data in a circle around the 
city, plus an extensive field program in which a number of State 
and Federal Government agencies and university research groups 

The objective of the second program was to prepare an environmen- 
tal impact statement on the effects of supersonic transport aircraft. 
The resulting research activity, the Climatic Impact Assessment Pro- 
gram (CIAP), involved 9 agencies and departments of the Federal 
Government, 7 agencies of other national governments, and over 1,000 
individual scientists in the United States and abroad. The program 
involved data-collecting activities using aircraft and balloons in the 
stratosphere, development of new techniques for sampling and measur- 
ing stratospheric pollutants, laboratory work in the photochemistry 
of atmospheric trace gases, measurement of pollutant emission by air- 
craft engines, mathematical modeling of stratospheric transport proc- 
esses and chemical reactions taking place there. 9 


It is a human tendency to cling to the belief that the natural environ- 
ment or climate to ivhich we have become accustomed will remain more 
or less the same from year to year and from decade to decade. We are 
surprised and alarmed tohen an unusually severe winter or an unusu- 
ally prolonged drought occurs, because our memories tend to be too 
short to recall past years when things were equally unusual. 

—William W. Kellogg, 1978 
National Center for Atmospheric^ Research. 

The facts are that climate everywhere does fluctuate quite noticeably 
from year to year and that there are gradual changes in climate that 
make one decade or one century different from the one before. These 
yearly fluctuations and longer term changes have been the result of 
natural processes or external influences at work on the complex system 
that determines Earth's climate. It is a system that seems to strive for 
a balance among atmosphere, oceans, land, and polar ice masses — all 

9 Barrett, Earl W., "Inadvertent Weather and Climate Modification." Crtiical Reviews in 
Environmental Control, vol. 6, No. 1, December 1975, pp. 15-90. 


influenced by possible solar and cosmic variations of which climate 
researchers' knowledge is in some cases nonexistent, or incomplete, and 
otherwise tenuous at best. Society itself is becoming another significant 
factor in the climatic balance. 

It is no news, for example, that the atmosphere of large midlatitude 
cities is both warmer and more turbid than the surrounding country- 
side (particularly in winter) as a result of thermal and chemical pol- 
lution and to some extent because of the ability of groups of buildings 
to trap heat from the Sun. There is also good evidence for increased 
summertime rainfall downwind from cities such as St. Louis, Chicago, 
and Paris. 10 Indeed, it is very likely that the industrialization of siz- 
able regions, such as the eastern United States and western Europe, 
has modified their climates in certain more subtle ways. In any attempt 
to assess a manmade climatic effect, it is essential to understand and 
have a measure of the degree of climatic variability which may be 
expected in the absence of human influence. 

The concept of climatic change and variability 

The concept of climatic change and variability entails a wide range 
of complex interactions with a disparity of response times among the 
air, sea, ice, land, and biotic components of the climate system. Climate 
is not a fixed element of the natural environment. Indeed, important 
advances in climate research and the study of former climates confirm 
that past climates of Earth have changed on virtually all resolvable 
time scales. This characteristic suggests that there is no reason to 
assume the favorable climatic regime of the last several decades is 
permanent and, moreover, that climatic change and variability must 
be recognized and dealt with as a fundamental property of climate. 

In this matter it is important to appreciate the fact that a renewed 
appreciation of the inherent variability of climate has manifested 
itself in the public consciousness. Climate has not become suddenly 
more variable in a way that it has never been variable before, but events 
of recent years 11 have shaken a somewhat false sense of technological 
invulnerability. Thus, climatic variability is a media item now because 
society ignored for so long its continued dependence on the ecological/ 
climatic balance achieved, and then failed to plan systematically for 
the coming unfavorable years, which eventually had to come — and 
always will, given the nature of the atmosphere. It is more palatable 
to blame climate for present predicaments than to acquiesce to a lack 
of preparedness. As F. Kenneth Hare, climatologist with the Science 
Council of Canada, has noted : 

It is paramount that the [climate- related] events of 1972 do not repeat them- 
selves, even if bad weather does. It does not matter whether such events are part 
of a genuine change in climate or are merely unusually large fluctuations of a 
basically unchanging system. In fact, I doubt whether such arguments mean any- 
thing. It does matter that climatic extremes do occur ; that they have recently 
become rather frequent and have had severe impacts ; that we lack the predic- 

10 Dettwiller, J. W. and S. A. Changnon, "Possible Urban Effects on Maximum Daily 
Rainfall Rates at Paris, St. Louis, and Chicago." Journal of Applied Meteorology, vol. 15, 

May 1976. pp. 517-519. 

11 Most of the world's important grain-growing regions experienced unfavorable weather 
and crop failures in 1972 or 1974. or both. Tbo winter of 1977 was perceived by most Amer- 
icans as remarkably abnormal, with severe cold in the East (coldest, in fact, since the 
founding of the Republic), drought in the West, and mild temperatures ns far north as 
Alaska : and the summer of 1977 was one of the two or three hottest in the last 100 years 
over most of the United States. 


tive skill to avoid impacts on food production — and energy consumption; and 
that we [the atmospheric science community] are insufficiently organized to make 
maximum use of existing skill. 12 

While scientists concur that climate is not a fixed component of the 
natural environment, there is less agreement with regard to when 
and how climatic change occurs. Although in the long term a major 
natural change to a different climatic regime may be expected, it is 
unlikely that any trend toward such a change would be perceptible in 
the near term, as it could be obscured by large amplitude, shorter term 
climatic variability. Considered from a historical perspective, and 
judging from the record of past interglacial ages, climatic data indi- 
cate that the long-term trend over the next 20,000 or so years is toward 
a cooling cycle, a cooler climate, and eventually the next glacial age. 
The onset of that change may be a number of centuries or millennia 
away ; conceivably it may already have begun. In recent years, books 
and newspaper stories have conditioned us to expect colder weather in 
the future. In geological perspective, the case for cooling is strong. 
The modern-day world is experiencing an interglacial period, a rela- 
tively warm interlude — lasting many thousands of years — between 
longer intervals of cold. If this interglacial age lasts no longer than a 
dozen earlier ones in the past million years, as recorded in deep-sea 
sediments, we may reasonably suppose that the world is about due to 
begin a slide into the next ice age. It does seem probable, though, that 
this transition would be sufficiently gradual so that in the next 100 to 
200 years it would be almost imperceptible amid the ubiquitous varia- 
bility of climate. 13, 14 > 15 

Considering the much more recent past, climatologists point out 
that the world has been in the throes of a general cooling trend during 
the last SO or 40. years. Because this modern-day cooling trend has 
sometimes been misinterpreted as an early sign of the approach of an 
ice age (it really is only one of many irregular ups and downs of 
climate that mankind has witnessed through Jiistory ) , it has reenf orced 
the popular notion that our future is likely to be a cold one. (In point 
of fact, this cooling trend has been faltering in very recent years, and 
may already have started to reverse itself.) 

Writes research climatologist J. Murray Mitchell, Jr. : 

I agree with those climatologists who say that another ice age is inevitable. 
I strongly disagree, however, with those who suggest that the arrival of the next 
ice age is imminent, and who speak of this as the proper concern of modern 
civilization in planning for the next few decades or centuries. Should nature be 
left to her own devices, without interference from man, I feel confident in pre- 
dicting that future climate would alternately warm and cool many times before 
shifting with any real authority toward the next ice age. It would be these 
alternate warmings and coolings, together with more of the same ubiquitous, 
year-to-year variability of climate that has always been with us, that would be 
the appropriate object of our concerns about climate in the foreseeable future. 16 

12 Norwine, Jim, "A Question of Climate," Environment, vol. 19, No. 8, November 1977, 
p. 12. 

13 National Research Council, U.S. Committee for the Global Atmospheric Research Pro- 
gram, Understanding Climntic Change : A Program for Action, Washington, National 
Academy of.Sciences. 1975, 239 pp. 

14 U.S. Federal Council for Science and Technology Interdepartmental Committee for 
Atmospheric Sciences, report of the Ad Hoc Panel on the Present Interglacial, Washington, 
National Science Foundation. 1974. 22 pp. (ICAS lSb-FY75). 

15 United Nations. World Meteorological Organizations (WMO). WMO Statement on Cli- 
matic Chance, pt. B : technical report, p 9. 

19 Mitchell J. Murray. Jr.. "Carbon Dioxide and Future Climate," EDS [Environmental 
Data Service] magazine, March 1977, p. 4. 


Because of man's presence on the Earth, however, what will actually 
happen in future decades and centuries may well follow a different 
scenario ; imperceptibly different at first, but significantly so later on, 
covering a full spectrum of climatic possibilities ranging from warm- 
ing to cooling trends. Varying interpretations of this evidence have 
led, on one hand, to a scientifically valid caution regarding possible 
instability of present-day climate conditions and, on the other hand, to 
predictions that the Earth may be on the verge of a new climate regime, 
which implies a new equilibrium among the elements of the climatic 
system, involving a somewhat different set of constraints and, almost 
certainly, noticeable regional shifts of climate. Climate researchers 
iteratively emphasize the importance of recognizing and appreciating 
the inherent variability of climate, a fact which may be more signifi- 
cant than the uncertainty of whether recent events portend a trend 
toward a warmer or cooler climate of the future. 

When and how do climatic changes occur? 

So far, there is no single comprehensive theory, or even a combina- 
tion of a small number of theories, that completely explains — much less 
predicts — climatic fluctuations or change. As yet, there is no deter- 
ministic, predictive model of our planet's climate, and, until one is 
developed, predictions are as valid as the logic producing them. The 
periods of time involved in climatic predictions cover centuries, and 
the validity of climate forecasting is not easily tested. Nevertheless, 
there are some factors and processes that clearly should be taken into 
account, either in terms of observed correlations in the past or of 
theoretical assumptions about what should be important. All, in one 
way or another, effect changes and variability of climate by modifying 
the natural thermal balance of the atmosphere. 

One group of processes responsible for climatic change and varia- 
bility consists of external mechanisms, including: fluctuations of the 
Sun's radiative output, variations of Earth's orbital parameters, 
changes in atmospheric dust content, changes in levels of carbon diox- 
ide and ozone in the atmosphere, and migration of land masses and 
shifting of continental plates. 

In addition to being influenced by external forcing mechanisms, 
climate is, to a certain degree, regulated by processes internal to the 
climatic system, involving "feedback" interactions between the at- 
mosphere, the world ocean, the ice masses, the land surface, and the 
biosphere. If an external variable were to be changed by a certain fac- 
tor, the response of the climatic system to that change could be modi- 
fied by the actions of these internal processes which act as feedbacks 
on the climatic system modifying its evolution. There are some feed- 
backs which are stabilizing, and some which are destabilizing; that is, 
they may intensify deviations. 

In all likelihood, climatic change is a function of various combina- 
tions of interacting physical factors, external processes, internal proc- 
esses, and synergistic associations (see fig. 2), but it is not yet clear to 
what extent the observed variability of the climatic system originates 
from internal mechanisms, and to what extent from external mecha- 
nisms. It appears likely that the answer depends upon the time scale 
of variability, with internal processes probably important on the scale 
of months and decades, and external mechanisms becoming increas- 
ingly important on time scale's beyond a cent ury as depicted in figure 3. 


Changes of 
Solar Radiation 




H,0, N J( Oj, CO J( 3 , etc. 


atmosphere-land coupling atmosp here-ice coupling 

changes of 
atmospheric composition 

changes of land features, 
orography, vegetation, 
albedo, etc. 

Figure 2. — Schematic illustration of the components of the coupled atmosphere- 
ocean-ice-land surface-biota climatic system. The full arrows are ex- 
amples of external mechanisms, and the open arrows are examples of 
internal mechanisms of climatic change. 

Source: Living With Climatic Change. Proceedings of a conference/workshop held in 
Toronto, November 17-22, 1975. Ottawa, Science Council of Canada, 1976, p. 85. 

SoUr Variability 

Earth's Rotation, 
Polar Wandering 


Continental Drift 

Sea-Floor Spreading 
-* — Mountain Building 

Atmospheric Mass, Composition, Volcanic Dust 

♦ Orbital »- 


" Glaciers 

Continental Ice Sheets 

Sea Ice 


Sea-level, Lake Level, Isostatic Adjustment 

Oceanic Composition, 




-* Bottom — 



GLACIAL — Vegetal Cover 


Ocean Layer 

Man's Land Use 

-Pollutants, CO, 

Autovariation of 

of Atmosphere 

I I 



10 7 


10* 10* 10* 
Time in years 

10 3 


Figure 3.— Characteristic climatic events and processes in the atmosphere, hydro- 
sphere, cryosphere. lithosphere, and biosphere and possible causative factors or 
global climatic change. 

Source : National Research Council. U.S. Committee for the Global Atmospheric Research 
Program. Understanding Climatic Change : A Program for Action. Washington, National 
Academy of Sciences, 1975, p. 22. 


For a comprehensive and detailed discussion of the mechanisms and 
factors governing climatic change and variability, see "A Primer on 
Climatic Variation and Change" ( 1976) . 17 

The possibility also exists that society may be changing the climate 
through its own actions by pushing on certain leverage points. Our 
presence on Earth cannot be assumed to go unnoticed by the atmos- 
phere, and human intervention now presents possibilities that have 
never existed in the historic or geologic past. At question is whether 
the effects of civilized existence are yet capable of altering Earth's 
heat balance and, hence, impacting climate on a global scale to an im- 
portant extent. Enormous amounts of gaseous and particulate mate- 
rials have been emitted into the atmosphere through the combustion 
of fossil fuels (primarily carbon dioxide, sulfur dioxide, and fly ash) 
and through the manipulation of land for agriculture and commerce 
(primarily windblown dust, and forest and grass fire smoke). To 
an increasing extent, waste heat is also entering the atmosphere, both 
directly and indirectly (via rivers and estuaries) and in both sensible 
and latent form (as, for example, through evaporation in wet cooling 
towers). Moreover, large-scale land management programs have been 
responsible for significant changes in reflective properties, moisture 
holding capacity, and aerodynamic roughness of the surface (pri- 
marily through deforestation, water impoundment by manmade lakes, 
slash-burn agriculture practices, urbanization, and so forth). In view 
of the growth of population, industry, food production, and commerce 
in the years and decades ahead, the time is almost certainly not far 
off when human effects on large-scale climate would become appreci- 
able in relation to natural phenomena leading to changes and vari- 
ability of climate. 

It does seem likely that industrial man already has started to have 
an impact on global climate, although this is difficult to prove by direct 
observation, because the impact is not easily recognizable amid the 
large natural variability of climate. "If man continues his ever- 
growing consumption of energy," contends J. Murray Mitchell, "and 
in the process adds further pollution to the global atmosphere, it may 
not be very many years or decades before his impact will break through 
the 'noise level' in the record of natural climatic variability and 
become clearly recognizable." 18 Furthermore, the most significant 
impacts that mankind would probably have on the climatic system 
are apparently all in the same direction as far as global mean tempera- 
tures are concerned and are likely to constitute a warming trend. 19 

The Facts About Inadvertent Weather and Climate Modification 
airborne particulate matter and atmospheric turbidity 

Particulate matter in the atmosphere may significantly affect climate 
by influencing the Earth's radiation balance (figure 4) and/or cloud 
nucleation and precipitation. 

17 Justus. John R.. "Mechanisms and Factors Governing Climatic Variation and Change.'' 
In "A Primer on Climntic Variation and Change," prepared by the Congressional Research 
Service, Library of Congress, for the Subcommittee on the Environment and the Atmosphere 
of the Committee on Science and Technology. U.S. House of Representatives. 94th Cong., 
2d sess. (committee print). Washington. U.S. Government Printing Office, 197G, pp. 77-127. 

18 Mitchell, J. Murrav. Jr.. "Carbon Dioxide and Future Climate," p. 4. 

Jt > Kellogg. William W.. "Is Mankind Warming the Earth?" Bulletin of the Atomic Scien- 
tists, vol. 34, February 1978, pp. 10-19. 


Do more particles mean a warming or cooling? 

There is a question as to whether more particles mean a warming 
or cooling of the lower atmosphere. The general cooling trend of the 
last 30 to 40 years (which some experts feel may have bottomed out 
and already started to reverse itself) could have been a result of a 
reduction of solar radiation reaching the surface of the Earth because 
of particulates that have been scattered into the atmosphere by man's 
activities, among them : the burning of fossil fuels, mechanized agri- 
cultural operations, overgrazing of arid lands, manmade forest fires, 
and the slash -burn method of clearing land for crops, which is still 
widely employed in the Tropics. But if man started his polluting 
processes in the last century, and the decrease of global temperature 
were due to alteration in the transparency of the atmosphere, then 
why has a decrease in temperature not been observed earlier? It is 
possible that instruments were measuring a natural climatic trend 
that may have been only somewhat augmented by the byproducts of 
resource development, power generation, and industrial activities. 

The situation is such that the net effect of a given particle on Earth's 
heat balance and hence on climate depends, in large part, upon the 
nature (number and size) of the particles, where in the atmosphere 
they are found, and how long they remain suspended. Some aerosols, 
such as lead from auto exhaust, are rapidly scavenged by precipitation. 
Others, mostly organic particles such as pesticides, may remain for 
months or years. While short-term aerosols such as lead may affect 
weather on a local scale, it is the aerosols that remain and accumulate 
in the atmosphere that will have long-term effects on climate. 

Figure 4. — The mean annual radiation and heat balance of the atmosphere, 
relative to 100 units of incoming solar radiation, based on satellite measure- 
ments and conventional observations. 

Source : National Research Council. U.S. Committee for the Global Atmospheric Research 
Program. Understanding Climatic Change : A Program for Action, Washington, National 
Academy of Sciences, 1975, p. 18. 

34-857 O - 79 - 13 


Idso and Brazel reporting on their research results in the November 
18, 1977 issue of Science magazine found that initial increases in 
atmospheric dust concentration tend to warm the Earth's surface. 
After a certain critical concentration has been reached, continued dust 
buildup reduced this warming effect until, at a second critical dust 
concentration, a cooling trend begins. But, they explain, this second 
critical dust concentration is so great that any particulate pollution of 
the lower atmosphere will have the inexorable tendency to increase 
surface temperatures. The authors pointed out that if, and when, man- 
generated, industrial pollution of the atmosphere as a source of par- 
ticulates ever becomes climatologically significant, the resultant sur- 
face temperature trend will definitely be one of warming, not cooling. 
Thus, whereas many groups assigned to assess the problem have looked 
on this aspect of intensified industrialization as acting as a "brake" 
on the warming influence inferred lately of increased carbon dioxide 
production, 20 just the opposite is actually the case — the two phenomena 
could tend to complement each other. 21 

Sources of atmospheric particulates: natural against manmade 

Of course, not all aerosols in the Earth's atmosphere, or even a major 
proportion, are attributable to human activity. In fact, dust from vol- 
canic eruptions, sea salt from evaporated ocean spray, smoke from 
lightning-caused forest fires (see fig. 5), debris from meteors which 
burn up in the atmosphere, windblown dust or sandstorms, and organic 
compounds emitted by vegetation are much larger sources of atmos- 
pheric particulates than human activity. Scientists at Stanford Uni- 
versity estimate that natural processes produce about 2,312 million 
tons of aerosols a year, which amount to 88.5 percent of the total. 
Man and his activities account for only 296 million tons, the remaining 
11.5 percent. At present, it is unlikely that man's activities and man- 
made aerosols will affect global temperatures. It is important to note, 
however, that while aerosols from natural sources are distributed 
fairly evenly across the planet, man, in contrast, contributes high con- 
centrations mostly from industrial centers. Atmospheric scientists at 
the National Oceanic and Atmospheric Administration's Atmospheric 
Physics and Chemistry Laboratory found that the 296 million tons of 
manmade aerosols are produced every year on only about 2.5 percent 
of the surface of the globe. Within these limited areas, manmade 
aerosols account for nearly 84 percent of the total. It follows, then, 
that these aerosols may be expected to have noticeable effects on local 
weather and urban climates. 

20 See, generally, National Research Council. Geophysics Research Board, "Energy and 
Climate," Washington, National Academy of Sciences, 1977, 281 pp. 

21 Idso, Sherwood B. and Anthony J. Brazel, "Planetary Radiation Balance RB a Function 
of Atmospheric Dust : Climatological Consequences," Science, vol. 198, Nov. 18, 1977, pp. 


Figure 5. — Not all aerosols in the Earth's atmosphere are attributable to human 
activity. In this Landsat photo, smoke from a fire in the Seney National Forest, 
upper peninsula of Michigan, serves as a source of atmospheric particulates. 
Note the extent of the dust veil downwind of the source. ( Courtesy of National 
Aeronautics and Space Administration. ) 

Atmospheric processes affected by particles 

Everyday, particles of soot, smoke, dust, and chemicals from indus- 
trial combustion and other activities are emitted into the urban atmos- 
phere. About 80 percent of the solid contaminants are small enough to 
remain suspended in the air, sometimes for several days. 22 Even though 
these tiny particles reflect and scatter sunlight ostensibly keeping its 
heat from reaching the ground, they also can act as a lid to prevent 
the outflow of heat from the land surface to the atmosphere. In a sense, 
this turbidity acts as an insulator. It reduces the amount of sunlight 
received at the top of the city in the daytime and cuts down on a source 
of heat. However, at night urban aerosol pollutants retard the depar- 
ture of radiant energy from the heated city air, encasing the heat in 

22 "Do Cities Change the Weather?" Mosaic, vol. 5, summer 1974, pp. 33, 34. 


the city's closed atmospheric system. Certain aerosols may undergo 
chemical change when they combine with water vapor in the presence 
of solar radiation. There are many complicated processes that can 
generate aerosol gas-to-particle conversions, and the particles can then 
grow by surface chemistry and physical accretion. 23 

Perhaps the most sensitive atmospheric processes which can be 
affected by air pollutants are those involved in the development of 
clouds and precipitation. The formation and building of clouds over 
a city can be influenced by the presence of pollutants acting as nuclei 
upon which water vapor condenses and by the hot dry air with which 
these aerosols are swept into the base of the clouds (see fig. 6). The 
structure of clouds with temperatures below 0° C (defined as cold 
clouds) can be modified, and under certain conditions precipitation 
from them altered, by particles which are termed ice nuclei. 24 The con- 
centrations of natural ice nuclei in the air appear to be very low : Only 
about one in a billion atmospheric particles which are effective as ice 
nuclei at temperatures above about — 15° C have the potential for mod- 
ifying the structure of clouds and the development of precipitation. 
If the concentration of anthropogenic ice nuclei is about 1 in 100 mil- 
lion airborne particles, the result may be an enhancement of precipita- 
tion ; however, if the concentration is greatly in excess of 1 in 100 mil- 
lion, the result may be a tendency to "overseed" cold clouds and reduce 
precipitation. Certain steel mills have been identified as sources of ice 
nuclei. Also of concern is the possibility that emissions from automo- 
biles may combine with trace chemicals in the atmosphere to produce 
ice nuclei. 25 

23 Hobhs. P. V.. H. Harrison, E. Robinson, "Atmospheric Effects of Pollutants." Science, 
vol. 183, Mar. 8, 1974. p. 910. 

2i National Research Council. Committee on Atmospheric Sciences. "Weather and Climate 
Modification : Problems and Progress," Washington, National Academy of Sciences, 1973, 
pp. 41-47. 

25 Hobbs, P. V., H. Harrison, E. Robinson, "Atmospheric Effects of Pollutants," p. 910. 


Figure 6. — The formation and building of clouds can be influenced by the pres- 
ence of pollutants acting as nuclei upon which water vapor condenses and by the 
hot dry air with which these aerosols are swept aloft. In this Landsat photo, 
excess particles as well as heat and moisture produced by the industries of Gary, 
Ind.. favor the development of clouds downwind. The body of water shown is 
the southern tip of Lake Michigan. (Courtesy of National Aeronautics and 
Space Administration.) 

Precipitation from clouds that have temperatures above 0° C (warm 
clouds) may be modified by particles which serve as cloud condensa- 
tion nuclei (CCN). A source that produces comparatively low con- 
centrations of very efficient CCN will tend to increase precipitation 
from warm clouds, whereas one that produces large concentrations 
of somewhat less efficient CCN might decrease precipitation. Modi- 
fications in the structure of clouds and precipitation have been observed 


many miles downwind of fires and pulp and paper mills. Large wood- 
waste burners and aluminum smelters have also been identified as 
major sources of CCN. 26 

The La Porte tveather anomaly: urban climate modification 

La Porte, Ind., is located east of major steelmills and other indus- 
tries south of Chicago. Analysis of La Porte records revealed that, 
since 1925, La Porte had shown a precipitation increase of between 
30 and 40 percent. Between 1951 and 1965, La Porte had 31 percent 
more precipitation, 38 percent more thunderstorms, and 246 percent 
more hail days than nearby weather stations in Illinois, Indiana, 
and Michigan. 27 Reporting on this anomaly at a national meeting of 
the American Meteorological Society in 1968, Stanley Changnon, a 
climatologist with the Illinois State Water Survey pointed out that 
the precipitation increase in La Porte closely followed the upward 
curve of iron and steel production at Chicago and Gary, Ind. Fur- 
thermore, La Porte's runs of bad weather correlated closely with 
periods when Chicago's air pollution was bad. Stated simply, Ohang- 
non's theory was that if this effect did not occur by chance, then the 
increase in precipitation comd be caused by the excess particles 
as well as heat and moisture produced by the industries upwind 
of La Porte. Pollutants from the industrial sources, it seemed, were 
serving as nuclei to trigger precipitation, just as silver iodide crystals 
are used to seed clouds in deliberate efforts of weather modification. 28 
The discovery of the La Porte anomaly helped usher in considerable 
scientific and public concern as to whether cities could measurably 
alter precipitation and severe weather in and downwind of them. A 
large urban-industrial center is a potential source of many conditions 
needed to produce rainfall. These include its release of additional 
heat (through combustion and from "storage" in surfaces and build- 
ings) which lifts the air ; the mechanical mixing due to the "mountain 
effects" of a city existing in flat terrain ; additional moisture released 
through cooling towers and other industrial processes ; and the addi- 
tion of many small particles (aerosols), which could serve as nuclei 
for the formation of cloud droplets and raindrops. 

The interest in whether urban emissions into the atmosphere could 
trigger changes in weather and climate on a scale much larger than 
the city itself led to climatological studies of other cities. Historical 
data for 1901-70 from Chicago. St. Louis, Washington, D.C., Cleve- 
land, Xew Orleans, Houston, Indianapolis, and Tulsa were studied in 
an effort to discern whether cities of other sizes, different industrial 
bases, and varying climatic-physiographic areas also experienced rain- 
fall changes. The six largest cities — Washington, Houston, New 
Orleans, Chicago, Cleveland, and St. Louis — all altered their summer 
precipitation in a rather marked fashion: Precipitation increases of 
LOto 30 percenl in and downwind of t heir urban locales, plus associated 
increases in thunderstorm and hailstorm activity were documented. 

16 National Research Council. Committee on Atmospheric Sciences, "Weather and Climate 
Modification : Prohlems and Progress." p. 50. 

» Lansford. Henry, "We're Changing the Weather hy Accident," Science Digest, vol. 74, 
Dec. 1973, p. 21. 

M Changnon. S. A., Jr.. "The La Porte Weather Anomaly — Fact or Fiction?" Bulletin of 
the American Meterologlcal Society, vol. 49, January 19G8, pp. 4-11. 


Tulsa and Indianapolis, cities of lower population and lesser physio- 
graphic irregularities than the others studied, did not reveal any 
precipitation anomalies. 29 

The key questions that could not be answered conclusively at the 
completion of these climatic studies were (1) whether the anomalies 
found were real (or adequately measured) ; (2) if real, what was 
causing the anomalies; and (3) whether and how extensive the anoma- 
lies were around other cities. To this end, a major atmospheric pro- 
gram dealing with inadvertent weather modification was initiated 
by a group of scientists in 1971. The Metropolitan Meteorological 
Experiment (METROMEX) was designed by four research groups 
who received support from Federal agencies and one State (Illinois). 
St. Louis was chosen as the site of extensive field investigations in this 
first major field program aimed at studying the reality and causes of 
urban rainfall anomalies suggested in the climatological surveys con- 
ducted previously. 30 

Although data analysis and report preparation continue (summer 
1975 was the fifth and final year for field work), METROMEX data 
thus far portray statistically significant increases in summer rainfall, 
heavy (more than 2.5 cm) rainstorms, thunderstorms and hail in and 
just east (downtown) of St. Louis. Examination of the rainfall yield of 
individual showers, the spatial distribution of rain developments, and 
areal distribution of afternoon rain clearly point to the urban-indus- 
trial complex as the site for the favored initiation of the rain process 
under certain conditions. 31 

Writes climatologist Stanley Changnon : 

The greater frequency of rain initiations over the urban and industrial areas 
appears to be tied to three urban-related factors including thermodynamic 
effects leading to more clouds and greater in-cloud instability, mechanical and 
thermodynamic effects that produce confluence zones where clouds initiate, and 
enhancement of the [raindrop] coalescence process due to giant nuclei. Case 
studies reveal that once additional [rainstorm] cells are produced, nature, cou- 
pled with the increased likelihood for merger with more storms per unit area, 
takes over and produces heavier rainfalls. Hence the city is a focal point for 
both rain initiation and rain enhancement under conditions when rain is likely. 31 

Recapitulating, METROMEX researchers have found that rain, 
thunderstorms and hail can actually maximize within cities and nearby 
areas, particularly in those downwind. Such locations may have more 
storms, and they are more intense, last longer and produce more rain 
and hail than storms in surrounding regions. Apparently, air heated 
and polluted by a city can move up through the atmosphere high 
enough to affect clouds. This urban-modified air clearly adds to the 
strength of convective storms and increases the severity of precipita- 
tion. Urban climatic alterations are summarized in table 1. 

29 Huff, F. A. and S. A. Changnon, Jr., "Precipitation Modification by Major Urban Areas," 
Bulletin of the American Meteorological Society, vol. "54, December 1973, pp. 1220-1232. 

30 Changnon. S. A., F. A. Huff, and R. G. Semonin, "Metromex : An Investigation of 
Inadvertent Weather Modification," Bulletin of the American Meteorological Society, vol. 
52, October 1971, pp. 958-967. 

si "METROMEX Update," Bulletin of the American Meteorological Society, vol. 57, March 
1976, pp. 304-308. 

32 Changnon, S. A., R. G. Semonin and F. A. Huff, "A Hypothesis for Urban Rainfall 
Anomalies," Journal of Applied Meteorology, vol. 15, June 1976, pp. 544-560. 


Table 1. — Some urban climatic alterations 1 

Comparison with rural environs 

Radiation : 

Global 10 to 20 percent less. 

Ultraviolet : 

Low sun 30 to 50 percent less. 

High sun 5 to 10 percent less. 

Temperature : 

Annual mean 1 to 2° C higher. 

Maximum difference 3 to 10° C higher. 

Winter minima 1 to 3° C higher. 

Cloudiness : 

General cloud cover 5 to 10 percent more. 


Winter 100 percent more. 

Summer 20 to 30 percent more. 

Precipitation : 
Totals : 

Summer 10 percent more. 

Winter 5 percent more. 

Relative humidity : Annual mean 4 to 6 percent less. 

Evapotranspiration : Total amount 30 to 60 percent less. 

Dew : Amounts 50 to 80 percent less. 

Wind speed : < 3 m sec -1 40 percent less. 

Speeds : 

3 — 6 m sec 20 percent less. 

> 6 m sec 10 percent less. 

Thunderstorms : Number of days 5 to 10 percent more. 

1 After Helmut Landsberg, University of Maryland. 


The constituent gases of the atmosphere that are important vari- 
ables affecting the distribution of temperature within the atmosphere 
are carbon dioxide and water vapor. Capable of absorbing important 
quantities of infrared radiation, they both have a role in modifying 
the vertical distribution of temperature in the atmosphere by con- 
trolling the flux of infrared radiation. The absorption of incoming 
solar radiation by these gases is so small that their concentration has 
no appreciable effect on the amount of incoming solar radiation reach- 
ing the Earth's surface. Carbon dioxide and water vapor are, how- 
ever, opaque to major portions of the long- wave radiation emitted by 
the Earth's surface. The greater the content of these gases the greater 
the opacity of the atmosphere to infrared radiation and the higher its 
temperature must be to radiate away the necessary amount of energy 
to maintain a radiation balance. It is this absorption of long-wave 
radiation emitted by the Earth, with the subsequent reradiation of 
additional infrared radiation to the ground and consequent elevation 
of air temperatures near the surface that is known as the "greenhouse 

Increases in atmospheric c<trhon diowide concentration: what the 
record indicates 

Man adds carbon dioxide to the atmosphere through the combustion 
of fossil fuels, and this addition is superimposed on the natural ex- 
changes between the atmosphere, the biosphere, and the world ocean. 
Since the use of energy has increased exponentially since the beginning 


of industrialization around 1860, it is not surprising that the best 
estimate of carbon dioxide production, which results from fossil fuel 
combustion and cement manufacture, shows the same exponential 
trend (see fig. 7). 

The concentration of carbon dioxide in the atmosphere has in- 
creased steadily from a preindustrial value of about 295 parts per 
million in 1860 to a current value of 330 parts per million (+ 12 
percent). Since the beginning of accurate and regular measurements 
in 1958, observed atmospheric carbon dioxide concentrations have in- 
creased some 5 percent from 315 parts per million to the current yearly 
average value of 330 parts per million as indicated in figure 8. 

Figure 7. — The annual world production of carbon dioxide from fossil fuels (plus 
a small amount from cement manufacture) is plotted since the beginning of 
the industrial revolution. Except for brief interruptions during the two world 
wars and the Great Depression, the release of fossil carbon has increased at a 
rate of 4.3 percent per year. (Data for 1860-1959 from C. D. Keeling, "Indus- 
trial Production of Carbon Dioxide from Fossil Fuels and Limestone," Tellus, 
vol. 25, 1973, p. 174 ; data for 1960-71 from R. M. Rotty, "Commentary on and 
Extension of Calculative Procedure for Carbon Dioxide Production," Tellus, 
vol. 25, 1973, p. 508.) 

Source : Baes. 'C. F.. et al. "The Global Carbon Dioxide Problem," Oak Ridge National 
Laboratory, 1976. (ORNL-5194.) 


Figure 8. — Monthly average values of the concentration of carbon dioxide in the 
atmosphere at Mauna Loa Observatory, Hawaii, are plotted since the beginning 
of accurate and regular measurements in 1958. Variations in photosynthesis and 
other seasonal effects produce the annual cycle. Mean annual concentrations 
are well above the preindustrial level (290-300 ppm), and the secular increase 
is quite apparent. 

Source: Baes, C. F., et al. "The Global Carbon Dioxide Problem," Oak Ridge National 
Laboratory, 1978. (ORNL-5194.) 

The seasonal variation of the record of carbon dioxide measurements 
made at Mauna Lao is obvious and regular, showing an October mini- 
mum with increases in the later autumn and winter months and a maxi- 
mum in May. However, of greater importance to possible climatic 
changes is the continued year-to-year rise. Both the seasonal variation 
and the annual increase have been confirmed by measurements at other 
locations around the globe. 

Predicting future atmospheric carbon dioxide levels 

Projecting the worldwide needs for energy, even with the present 
problems, indicates a long-term global growth in the consumption of 
fossil fuels and the associated production of carbon dioxide. Insofar as 
possible impact on the climate is concerned, it is the amount of carbon 
dioxide remaining in the atmosphere that is most important. In addi- 
tion to the atmosphere, the ocean and both land and marine biospheres 
serve as reservoirs for carbon dioxide. Based on estimates of preindus- 
trial levels of atmospheric carbon dioxide of 290-295 parts per million 
and the 1958 to present Mauna Loa data, between 58 and 64 percent of 
the carbon dioxide produced from burning fossil fuels remains in the 
atmosphere. Cumulative production of carbon dioxide is plotted in 
figure 9. The upper set of points indicates the increase in the carbon 
dioxide fraction of the atmosphere that would have occurred if all car- 


bon dioxide produced since 1860 from fossil fuels and cement remained 
airborne. The lower set of points represents the observed increase based 
on an assumed value of 290-295 parts per million in 1860. The differ- 
ence between the two sets of points presumably indicates the amount of 
carbon dioxide being taken up by the world ocean and possibly the 
biosphere and placed in long-term storage. Nearly half of the carbon 
dioxide produced from fossil fuels and cement seems to have found its 
way into reservoirs other than the atmosphere. 

1 r 

n r 

i ! 1 1 1 i i r 

9 S\c9*- 

I860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 


Figure 9. — The cumulative production of carbon dioxide since 1860 is compared 
with the observed increase in the mean annual concentration since that time. 
The similarity in the rates of increase (about 4 percent per year) produces 
strong evidence that these two quantities are related. About 50 percent of the 
fossil carbon flux apparently has been balanced, at least since 1958, by a 
flow of carbon dioxide to such reservoirs at the world ocean and/or the land 
biota (assumed 1860 atmospheric concentration equals 295 ppm) . 

Source : Baes. C. F., et al. "The Global Carbon Dioxide Problem," Oak Ridge National 
Laboratory, 1976. (ORNL-5194.) 

Future levels of atmospheric carbon dioxide will depend primarily 
on the rate of consumption of fossil fuel and to a lesser extent on land 
use patterns and practices. With brief interruptions for two world 
wars and the Great Depression, the production of carbon dioxide from 
fossil fuels has increased with an annual rate of 4.3 percent. 33 If the use 
of fossil fuels continues to grow at this present rate, the total carbon 
dioxide injected into the atmosphere by man since 1860 wouM reach 
300 parts per million by the year 2030, and the total concentration 
would be equal to 595 parts per million. This assumes, of course, no 
change in the average uptake by other reservoirs during this time. 
Those energy scenarios that rely heavily on coal, especially for syn- 
thetic oil and gas, yield estimated carbon dioxide concentrations of 

33 4.3 percent per year provides an excellent fit to the data in figure 7. 


600 parts per million about the year 2015 and 1,400 parts per miUion 
about 100 years from now. Rotty and Weinberg (1977) discuss a 
scenario by Niehaus in which nonfossil energy sources dominate soon 
after 2000. Even in this case the annual emission of carbon dioxide 
from fossil fuel peaks at about twice the present level in the year 2000 
and tapers off thereafter; the atmospheric concentration nevertheless 
reaches 475 parts per million by 2050. 34 ' 35 > 36 > 37 > 38 

Sources and sinks for carbon dioxide 

These extrapolations are based on certain assumptions, a critical 
one being that the ocean and the biosphere will continue to absorb a 
large fraction of the carbon dioxide in the atmosphere. Some ocean- 
ographers see increasing evidence that the upper mixed layer of the 
ocean, where most of the carbon dioxide is stored, is rapidly becoming 
saturated, and if this were true, then it tends to reenforce the attain- 
ment of relatively. high atmospheric carbon dioxide concentrations in 
the next century. However, this prediction is far from certain, because 
carbon dioxide absorption in the ocean could turn out to be greater than 
expected because of mixing between ocean layers or other factors. 39 
The problem is further complicated by a series of current appraisals 
that suggest that the terrestrial biomass appears to be a net source of 
carbon dioxide for the atmosphere. George M. Woodwell of the Marine 
Biological Laboratory at Woods Hole, Mass., explains : 

Over the past seven years several reviews of the world carbon budget have con- 
firmed that there is an annual increase in the carbon dioxide content of [the 
atmosphere] that is worldwide and is almost certainly man-caused. The source 
of the carbon dioxide that is accumulating in the atmosphere has been commonly 
assumed to be the combustion of fossil fuels. Because the amount of carbon diox- 
ide accumulating in the atmosphere is * * * [about] half the total released from 
fossil fuels, other sinks for carbon dioxide have been sought. The major sink is the 
ocean, but mixing rates appear to be too low for the oceans to accommodate all 
the carbon dioxide that is thought to be released in excess of that accumulating in 
the atmosphere. The question of whether the terrestrial biota could be another 
sjnk was raised in 1970 [at SCEP], and the assumption was made that the biota 
might be a sink, especially in view of the stimulation of photosynthesis under 
greenhouse conditions by enhanced concentrations of carbon dioxide. More re- 
cently, the assumption that increased carbon dioxide in air stimulates photo- 
synthesis worldwide has been questioned. So has the assumption that the biota 
is a net global sink for carbon dioxide. A series of current appraisals suggests 
that, quite contrary to the previous estimates, the biota is probably an addi- 
tional source of carbon dioxide * * * as large as or larger than the fossil fuel 
source. 40 

Thus, the great puzzle is the basic stability of the global carbon 
budget. Without better information on the behavior of the terrestrial 
biosphere, it is difficult to say whether the biosphere is a sink or a 
net source of carbon dioxide. If the biosphere is supplying more carbon 

34 Baes, C. F.. Jr.. et al. "The Global Cnrbon Dioxide Problem," Oak Ridge, Tenn., Oak 
Ridge National Laboratory. 1970. 78 pp. (ORNL 5194. ) 

* Lenkowski, Wil. "Carbon Dioxide: A Problem of Producing Usable Data." Chemical 
and Engineering News. vol. 55, Oct. 17, 1977 : pp. 26-30. 

;!0 Rotty, Ralph M.. "Energy and the Climate." Institute for Enerprv Analysis, Oak Ridge, 
Oak Ridge Associated Universities. 1970. 28 pp. ( ORAU/IEA (M) 75-3.) 

37 Rottv. R. M. and A. M. Weinberg. "How Long is Coal's Future," Climatic Change, vol. 1, 
No. 1. March 1977 : op. 45-57. 

3 * Rottv. Ralph M.. "The Atmospheric Carbon Dioxide Consequences of Heavy Dependence 
on Coal." Institute for Energy Analysis, Oak Ridge Associated Universities, occasional 
paper. 32 pp.. Nov. 14, 1977. 

39 Anthes. Ricbard A.. Hans A. Panofskv. John J. Cnbir and Albert Rango, "The Atmos- 
phere." Columbus. Charles E. Merrill Publishing Co., 197r>, p. 204. 

in YVoo''" eii (i. M.. ef al., "The Biota and the World Carbon Budget." Science, vol. 199, 
Jan. 13, 1978. pp. 141-146. 


dioxide than it is absorbing, then the behavior of the ocean must be 
different from what oceanographers believe, in the sense that it would 
be an even more effective sink for carbon dioxide than previously sur- 
mised. Thus, there is a need for intense examination of the flux of 
carbon into the ocean. The ability of the world ocean to act as a carbon 
dioxide sink is large, but the rate of possible sequestering of carbon is 
the important factor. One possibility is that biotic mechanisms in the 
ocean are more effective than has been assumed in transferring fixed 
carbon from the mixed (near-surface) Jayers of the ocean into deep 
ocean waters. Before an estimate can be made with confidence of what 
fraction of the carbon dioxide from fossil fuels remains in the atmos- 
phere, a better understanding of the roles of both the biosphere and 
the world ocean in the carbon cycle is necessary. 41, 42 - 43 

Atmospheric effects of increased carbon dioxide levels 

A change in the carbon dioxide content of the atmosphere upsets 
the Earth's radiation balance by holding back departing infrared light. 
All things being equal, if no other change were to occur in the system, 
the net amount of energy accumulated by the Earth would raise its 
surface temperature until the enhanced infrared emission reestab- 
lished balance between incoming and outgoing radiation. The problem, 
however, is greatly complicated by the fact that other changes would 
certainly take place. For example, if the Earth's temperature rises, 
the water vapor content of the atmosphere is likely to rise. More water 
will have the same effect as more carbon dioxide creating positive feed- 
back in the system and hence forcing temperatures to climb even higher. 
A rise in water vapor would quite likely increase the fraction of the 
globe covered by clouds. Such an increase would cause the amount of 
primary solar radiation absorbed by the Earth to fall. Some combina- 
tion of increased temperature and cloudiness will balance the enhanced 
absorption of infrared radiation by the added carbon dioxide and 
water vapor. 

Implications of increasing atmospheric carbon dioxide concentrations 
The possibilities and implications of a continued rise in the atmos- 
pheric carbon dioxide concentration were reviewed in a special report 
entitled ''Energy and Climate.*' released by the National Kesearch 
Council (NRC) on July 25, 1977. 44 

The most complete, though still imperfect, climate models suggest 
that a doubling of the amount of carbon dioxide in the atmosphere, 
relative to its present amount, would increase the average annual 
temperature of the lower atmosphere at middle latitudes by about 2.4° 
to 2.9° C (4.3° to 5.2° F), depending on which model is used to derive 
the estimated temperature change. 

Based on one climate model in which the hydrologic cycle is modeled 
in detail along with other aspects of climate behavior, a doubling of 
carbon dioxide has been calculated to result in about a 7 percent increase 

41 Bolin, Bert. "Changes of Land Biota and Their Importance for the Carbon Cycle ; The 
Increase of Atmospheric Carbon Dioxide Mav Partlv Be Due to the Expansion of Forestry 
and Agriculture." Science, vol. 196, May 6. 1977. pp. 613-615. 

"2 Siegreuthalpr. U and H. Oeschsrpr. "Predicting Future Atmospheric Carbon Dioxide 
Levels." Science, vol. 199, Jan. 27, 1978, pp. 388-395. 

43 WooriwHl. Geo-cre M., "The Carbon Dioxide Question," Scientific American, vol. 238, 
Janvary 1978. pp. 34-43. 

44 National Research Council. Geophysics Research Board, "Energy and Climate," Wash- 
ington, National Academy of Sciences, 1977, 281 pp. 


in global average precipitation. Most of this increase would be con- 
centrated in higher latitudes. A general retreat of snow and sea ice 
cover, by perhaps as much as 10 degrees of latitude, could result in 
the Arctic regions. The extent of such changes in the Antarctic, how- 
ever, has not been determined. The temperature rise is greater by a 
factor of three or four in polar regions than the average temperature 
change for the world as a whole. For each further doubling of carbon 
dioxide, an additional 3° C increase in air temperature is inferred. This 
would mean that should the carbon dioxide concentration approach 
four to eight times preindustrial levels, and increase in global mean air 
temperature of more than 6° C (11° F) could be realized — at which 
time Earth would be experiencing temperatures warmer than those at 
any time in the last million years. 45 

Implications of a climatic warming 

The implications for man-induced climatic warming are particularly 
far-reaching for agriculture, according to the NRC report. The global 
picture presented by the report is one dominated by the f orementioned 
gradual increase in mean air temperatures, with a concomitant shift- 
ing of agricultural zones, altered rainfall patterns and other major 
changes. Worldwide average annual precipitation could increase, 
which, at first glance, would seem to benefit agriculture. The accom- 
panying higher air temperature, however, would raise the rate of 
evapotranspiration from cultivated lands, and part of the benefits 
from the additional water supply could be lost. In some regions, 
evapotranspiration might exceed the increase in precipitation; in 
others, the reverse might be true. At higher latitudes, there would be 
a longer frostf ree growing season than at present, and the boundaries 
of cultivation could be extended northward in the Northern Hemi- 
sphere. Attendantly, summer temperatures might become too high for 
full production of middle-latitude crops such as corn and soy beans 
grown in Iowa, Illinois, Indiana, and Missouri, and it might be 
necessary to shift the Corn Belt toward the north where less produc- 
tive soils are encountered. Generally speaking, warmer temperatures 
would result in a poleward movement of agroclimatic zones. As the 
authors of the NRC report state : 

The most serious effects on agriculture would arise not from changes in global 
average conditions but from shifts in the location of climatic regions and changes 
in the relationships of temperature, evapotranspiration, water supply, cloudi- 
ness, and radiation balance within regions. Present cropping patterns, crop vari- 
eties, and farming technology in different climatic regions are based on cumula- 
tive experience over many years in the selection of appropriate crop species and 
varieties for each region and in adapting both the plants and their physical 
environment to each other in as nearly an optimal fashion as possible. These 
adaptations have remained fairly satisfactory over the relatively nam nge 
of climatic changes that have occurred in the historic past. But large el in 
climatic relationships within regions such as might be brought abo a 
doubling or quadrupling of atmospheric carbon dioxide would almost c _ily 
exceed the adaptive capacity of crop varieties grown at present. 46 

The potential global warming trend associated with increasing con- 
centrations of atmospheric carbon dioxide could increase desertifica- 
tion, 47 although there is not conclusive evidence for this possibility. 

*Mbid., pp. 4, 5. 

47 The awkward word "desertification" often refers to the process by which existing deserts 
spread but the term also may refer to the creation of desertlike conditions such as those 
which developed during the 1930's dust-bowl years in the North American Great Plains. 


The altered pattern of rainfall and temperature resulting from the 
release of carbon dioxide could change desert conditions in unexpected 
ways and even increase agricultural potential in some cases. Authors 
of the NRC report concede the present state of ignorance on the 
subject : 

The most serious effects of possible future climatic changes could be felt along 
the boundaries of the arid and semiarid regions in both hemispheres. We need to 
be able to estimate whether these belts of aridity and semiaridity will move 
toward or away from the poles and whether they will expand or contract in 
area. 48 

The effect of manmade or of natural climatic alteration of desert- 
areas is not clear. The advancement of desert conditions into agri- 
cultural areas in Africa and elsewhere has been documented during 
the past decade, and although rainfall patterns with associated wet 
and dry climates are controlled mainly by the general atmospheric 
circulation, human activities can have a marked effect on local desert 
conditions, even possibly intensifying the process of desertification and 
thereby compounding the problem. In particular, excessive ploughing 
of dry land or overenthusiastic introduction of livestock and expan- 
sion of cultivated areas, during wet periods, into marginal lands causes 
destruction of soil-protecting vegetation. During ensuing dry periods, 
these marginal lands, with their natural protective cover destroyed by 
cultivation and overgrazing, suffer loss of, or a decline in, the quality 
of soil. As this occurs over a large region, the bare dry ground, its 
reflectivity altered, now acts to intensify the natural climatic condi- 
tions which sustain the desert. 49 

Carbon dioxide and future climate: the real climate versus "model 

In the final analysis, it is well to remember that it cannot be asserted 
that a doubling of carbon dioxide in the real world would have the 
same effects on real climate as a simulated doubling of carbon dioxide 
in climate models would have on "model climate." This caveat is in 
order because no climate model is altogether realistic in its description 
of the real climatic system, and because some of the physical processes 
that operate in the real climatic system cannot yet be simulated at all 
in climate models. Comments J. Murray Mitchell, Jr. : 

No climate model on which the above conclusions [regarding climatic warm- 
ing] are based is capable of developing its own cloud systems in a realistic 
way : most models must be instructed before hand where the clouds are assumed 
to exist, and the clouds remain there unchanged throughout the computer 
experiment using the model. We should be wary of this, because if the cloudi- 
ness were to change in the real world along with a carbon dioxide change, 
then the role of clouds in affecting the temperature of the Earth might sig- 
nificantly alter the net temperature effect of the carbon dioxide change as 
inferred from models that assume fixed cloudiness. 50 

the model is allowed to adjust cloudiness along with other weather 
variables as the calculation proceeds. Early indications are that 
Some preliminary model experiments have been attempted at the 
National Oceanic and Atmospheric Administration's (NOAA) Geo- 
physical Fluid Dynamics Laboratory in Princeton, N.J., in which 

48 National Research Council, Geophysics Research Board, op. cit., p. 14. 
48 Ibid. 

50 Mitchell, J. Murray, Jr., "Carbon Dioxide and Future Climate," p. 9. 


allowance for cloudiness changes does not greatly alter the results of 
experiments using models with fixed cloudiness. 

Altogether, the experience with climate models suggests that their 
use in evaluating the magnitude of temperature changes associated 
with changes of atmospheric carbon dioxide leads to results that are 
likely to approximate reality fairly closely. Models may be overesti- 
mating the temperature and other climatic effects of carbon dioxide 
changes by as much as a factor of two. On the other hand, it is 
equally likely that they may be underestimating the effects by a 
factor of two. In balance, the model results to date warrant being 
taken as an unprejudiced and credibly realistic approximation to 
reality. 51 


The concern that man's activities could in some fashion change the 
stratosphere first emerged as a public issue during the debate on the 
American SST in 1969. The American SST program was, at that 
time, almost a decade old and was approaching its final phase when 
it was challenged by a coalition of more than 30 environmentally 
oriented organizations. The environmentalists contended that the 
SST, flying in the stratosphere, would contaminate the stratosphere 
and alter its characteristics. The dominant concern was that water, 
created as a product of fuel combustion, would interact with the 
stratospheric ozone and destroy it. 

Concerns regarding ozone destruction 

Ozone (0 3 ) exists everywhere in the atmosphere and reaches a 
maximum concentration at around 80,000 feet. It is created, as well 
as destroyed, by the interaction of ultraviolet light from the Sun with 
oxygen molecules in the upper atmosphere. Most of the ozone is 
created in the Tropics and is dispersed from there toward both poles. 
Due to the destructive action of sunlight and to the atmospheric 
transport systems, the Tropics, where most of the ozone is made, have 
the least dense coverage of ozone. Ozone density increases in the 
temperate zones and reaches its maximum density in the polar regions. 
Ozone density over a given spot on Earth may vary as much as 25 
to 30 percent on a given day and as much as 300 percent throughout 
the year depending on the season. Ozone density measurements have 
shown that the Northern Hemisphere of the Earth has a slightly 
denser coverage than the Southern Hemisphere. 

The importance of the ozone content of the upper atmosphere 
centers on the fact that the ultraviolet light that creates ozone is 
absorbed in the process. These wavelengths of ultraviolet light are 
damaging to life of all sorts if the intensity is too great. It should be 
noted that some ultraviolet light is required by animal life to produce 
vitamin D which gives protection against rickets. 

In the debate over the American SST, it became clear that neither 
side had enough data on the stratosphere to refute the other. Despite 
this, the debate remained lively for more than a year and was finally 
terminated by the congressional decision to cancel the SST program 
and to initiate programs to study the upper atmosphere and in par- 
ticular, its ozone. 

51 Information gleaned In a session on "climatic futures" at the 1978 annual meeting of 
the American Association for the Advancement of Science in Washington, D.C., Feb. 17, 


Congress requested and funded a 3-year, $24 million program, to 
determine whether or not the stratospheric flight constituted a threat 
to the Earth's environment. Responsibility for the study was given to 
the Department of Transportation and was called the "Climatic Im- 
pact Assessment Program" (CIAP). 52 The theoretical mechanisms 
which indicated that water, created from the combustion of fuel, would 
mix with and destroy ozone appeared to be reasonable and meritorious 
of serious study. Early in the CIAP, however, actual measurements of 
ozone density in the stratosphere in volumes of air which were per- 
meated by the plume from jet engines, were made. These measurements 
showed that ozone density seemed to increase subsequent to the injec- 
tion of water vapor. Why this occurs is not yet understood, but the test 
provided adequate information to conclude that water vapor injected 
into the stratosphere would not constitute a danger to the ozone. 

During the conduct of the CIAP program, other papers began to 
appear which described a variety of heretofore unconsidered theoreti- 
cal ways in which man's activities could adversely effect the ozone 
density in the stratosphere. The atmosphere of the Earth is about 80 
percent nitrogen and 20 percent oxygen. The oxygen used in the com- 
bustion process is therefore accompanied by a large amount of nitro- 
gen. The heat of combustion causes the formation of several oxides of 
nitrogen (NO x ). Theoretical mechanisms were proposed which pre- 
dicted that the NO x formed in the stratosphere by a jet engine would 
mix with the ozone and destroy it in a catalytic manner. In other 
words, during the process in which the NO x would destroy the ozone, 
the XO x would be reformed and released to destroy still more ozone 
in a continuous manner. 53 The mechanisms for this process appeared 
reasonable and worthy of serious study. However, Dr. John J. 
McKetta of the CEQ noted that the total NO x burden produced by 
combustion processes amounts to only about 2 percent of that produced 
by dying vegetation in the natural cycle of plant life. 54 It was then 
noted that the artificial insertion of nitrogen compounds into the soil 
for purposes of fertilizing caused the evolution and ultimate release 
of XO x in quantities amounting to a sizable fraction of that produced 
by nature. 55 • 56 

Moreover the bromine compounds used in agriculture as antifungi- 
cides were held to be even more potent in destroying ozone than NO x . 57 
Still more very large sources of NO x were identified, such as lightning 
from the some 5.000 storms around the Earth, each day. Also, air 
bursts of nuclear bombs produce NO x at the rate of 10,000 tons per 
megaton of yield. 58, 59 In the early 1960 ? s, 340 megatons of explosive 
injected about 3% million tons of XO x into the stratosphere. 

52 "Climatic Impact Assessment Program Development and Accomplishments, 1971-75," 
J. Mormino, et al., D0T-TST-76-41, December 1975. 

53 "Reduction of Stratospheric Ozone by Nitrogen Oxide Catalysts from Supersonic Trans- 
port Exhaust," H. Johnston, Science, Aug. 6, 1971. 

54 "The Eight Surprises," J. J. McKetta. address to the American Trucking Association, 
Oct. 16. 1974. reprinted in the Congressional Record. Mar. 12, 1975. 

55 "NOAA Scientist Weighs Possible Fertilizer Effects on Ozone," Paul Crutzen, Depart* 
ment of Commerce News, Apr. 15, 1975. 

56 "Nitrogen Fertilizer Threatens Ozone," quotes from J. McElroy, Washington Star, 
Dec. 12. 1974. 

57 "Weather Warfare" (Bromine). New Scientist, Mar. 27, 1975, p. 762. 

58 "Ozone Appears Unalterpd by Nitric Oxide," Kenneth J. Stein, Aviation Week and Space 
Technology, Nov. 6, 1972. p. 28. • • . ^ , r , 

. 59 "Nitrogen Oxides, Nuclear Weapon Testing, Concorde and Stratospheric Ozone," P. 
Goldsmith, et at, Nature, Aug. 31, 1973, p. 545. 

34-857—79 14 


It had begun to appear to many that, in the Earth's atmosphere, 
which' is about 80 percent nitrogen and 20 percent oxygen, the NOx is 
ubiquitous and that there was just no legislative way to save the ozone 
from the catalytic disintegration hypothesized. The issue endures 
largely as an academic debate, though its character could change again. 
One group holds that the destructive mechanisms ascribed to NO x are 
real and that ozone density is controlled by the presence of NO x - An 
opposing group contends that, while the hypothetical reactions appear 
to be sound, they just don't seem to occur. The insertion of 3% million 
tons of XO x by nuclear explosions over 1 year's time, for example, was 
judged by many as an experiment of sufficient magnitude to cause un- 
mistakable perturbations in ozone density, and would prove or dis- 
prove the destruction hypothesis. Recordings of ozone density before, 
during, and following the test were analyzed by numerous people. One 
investigator detected trends which he associated with the explosions ; 
however, others held that "the conclusion that massive injections of 
nitrogen oxides into the stratosphere do not upset the ozone layer seems 
inescapable." 60 

Putting that aside, yet another challenge to the ozone, the manmade 
fluorocarbons (freon aerosol propellants and refrigerants) has been 
postulated. 61 The hypothetical mechanisms by which these compounds 
would migrate into the stratosphere, break down to release odd chlorine 
molecules which would in turn set up a catalytic destruction of ozone, 
where examined and found to be plausible and a cause for concern. Sub- 
sequent measurements taken in the stratosphere proved the presence of 
numerous odd chlorine molecules, some of which could indeed be shown 
to have their origin in freon. 62 

Although the empirical validity of the destructive interaction of 
these odd chlorines with ozone is difficult to show and has yet to be 
shown, their discovery in the stratosphere was enough for several 
scientists to call for a ban on the fluorocarbons. Other scientists, as well 
as industry, took an opposing view, calling for empirical proof prior to 
taking actions to ban or control the manufacture or use of freon 

The argument became partly one of timing with one side claiming 
that no emergency could be proven and plenty of time was available to 
test the destruction hypothesis. Opposing this was the view that it may 
very well be too late already since most of the freons already released 
have yet to reach the stratosphere. 

Unlike the case with XO x . where changes as vast as banning the 
use of nitrating fertilizers might be required, the control of freon 
release was a manageable target for a regulatory control. The resulting 
studies and actions represent a model of rapid and cooperative action 
between a large number of highly diverse Government offices and 
agencies. The decision was made to act without waiting for empiricial 
proof of the destruction hypothesis, but not to institute the total and 
immediate ban some investigators called for. Instead, propellant ap- 
plication would be labeled as possibly hazardous to the ozone and then 

"° I '»id. 

r; "Stratospheric O^one Destruction hv Man-made Ohlorofluoromethanes," R. J. Cicerone, 
et al.. Science, Sept. 27, 1974. 

""Atmospheric Halocarbons and Stratospheric Ozone," J. E. Lovelock, Nature, Nov. 22, 


i banned in stages. Refrigerants would be studied pending their possible 
regulation at some future time. 

Action by the Government on the regulation of fluorocarbons 

The Council on Environmental Quality (CEQ) and the Federal 
Council for Science and Technology (FCST) reviewed theoretical 
oapers on the destructive interaction between fluorocarbons and ozone, 
the first of which appeared in 1974. They decided that the case was 
worthy of serious concern. In January 1975, the CEQ and FCST 
jointly created a large ad hoc task force known as the Federal Inter- 
agency Task Force on Inadvertent Modification of the Stratosphere 
(IMOS). IMOS membership included representatives from: 

Interdepartmental Committee for Atmospheric Sciences (ICAS). 

Department of Agriculture. 

Department of Commerce, 

Department of Defense. 

National Institute of Environmental Health Sciences. 

Food and Drug Administration. 

Department of Justice. 

Department of State. 

Department of Transportation. 

Energy Research and Development Administration. 

Environmental Protection Agency. 

Consumer Products Safety Commission. 

National Aeronautics and Space Administration. 

National Science Foundation. 

Council on Environmental Quality. 

Office of Management and Budget (observer only) . 

The work of IMOS was swift and orderly. A series of studies was 
completed and published in their report by June 1975. 63 IMOS con- 
cluded "that fluorocarbons released to the environment are a legitimate 
cause for concern." The report also referred to a similar study which 
was then underway at the National Academy of Sciences. IMOS rec- 
ommended that, should the results of the NAS study agree with their 
results, then Federal regulatory agencies should initiate rulemaking 
procedures for implementing regulations to restrict fluorocarbon uses. 

The data base for the NAS study was of course the same data base 
used by IMOS since it was the only one available. The conclusions 
reached by both studies were therefore the same, and rulemaking was 

If the data base could have contained some empirical proof sup- 
porting the validity of the massive ozone destruction hypothesis, the 
rulemaking procedures would have proceeded without, or at least with 
much less debate and protest. As it was, the rules were handed down 
without proof, the justification being that the consequences of higher 
UV exposure due to ozone thinning were sufficiently severe that pre- 
cautionary regulations were necessary. Under these circumstances, the 
rules Ave re models of compromise. A ban was to be issued over the pro- 
test of industry, but it would neither be the complete ban nor the imme- 
diate one demanded by the environmental groups and some scientists. 

63 '"Fluorocarbons and the Environment," IMOS. Council on Environmental Quality and 
the Federal Council for Science and Technology, June 1975. 


The proposed rules were formulated jointly by the Department of 
Health, Education, and Welfare, the Environmental Protection 
Agency, and the Consumer Product Safety Commission. In brief, they 

state : 

1. By October 15, 1978, no company may manufacture fluoro- 
carbons for use in aerosol products. 

2. By December 15, 1978, companies must stop using fluorocar- 
bons as propellants in aerosol products. 

3. As of April 15, 1979, no spray product containing a fluoro- 
carbon propellant may be introduced into interstate commerce. 
Products on store shelves at that time may be sold, however, and 
there will be no recall. 

4. Beginning in October 1978, warning labels will be put on 
aerosol products which contain fluorocarbons to warn the user 
that the fluorocarbons are present and may affect the ozone. 

5. Certain aerosol products intended for medical purposes are 
exempt from these regulations. 

The rule on labeling has already been put into effect. 64 

Climatic effects of ozone depletion 

While the effect of a significant buildup in the concentration of 
chlorofluorocarbons and chlorocarbons on the chemical balance of the 
Earth/atmosphere system is currently a subject of concern, their im- 
pact and effect on the Earth's overall thermal energy balance must 
also be considered. The chlorofluorocarbons and chlorocarbons have 
strong infrared absorption bands, thus allowing these compounds to 
trap long-wave radiation emitted by the Earth and, in turn, enhance 
the atmospheric "greenhouse effect." This enhancement may lead to 
an appreciable increase in global surface and atmospheric temperature 
if atmospheric concentrations of these compounds reach values of the 
order of 2 parts per billion (ppb) , 65 

Furthermore, ozone itself is important to the Earth's climate because 
it absorbs some quantities of both solar and terrestrial infrared radia- 
tion, thereby affecting the enerofv balance of the Earth/atmosphere 
system that determines the Earth's temperature. Exactly how changes 
in the ozone concentration might affect climate are far more difficult 
to determine, since changes in surface temperature from variations in 
ozone depend on such diverse factors as whether the total amount of 
ozone is increased or decreased, whether the height at which the maxi- 
mum amount of ozone occurs is altered, or whether the latitudinal 
distribution of ozone is disturbed. James Coakley of the National Cen- 
ter for Atmospheric Research (NCAR), Boulder, Colo., has found 
that a uniform reduction in the total amount of atmospheric ozone 
would lead to a cooling of the Earth's surface, but that a decrease in 
altitude in the stratosphere where ozone has its maximum concentra- 
tion can warm the surface. Similarly, an increase in total amount of 
ozouo warms, but an increase in the altitude of maximum ozone con- 
centration can cool the climate. If it were known that an atmospheric 

« The previous section on the ozone depletion Issue was contributed by George Chatham, 
Spprinllst In Aeronautics and Space, Science Policy Research Division, Congressional Re- 
peareh Service. 

* Rnmanathan. V., "Greenhousp Effect Due to Chlorofluorocarbons: Climatic Implica- 
tions" Science, vol. 190, Oct. 3, 1975, pp. 50, 51. 


pollutant, such as chlorofluorocarbons, acted to reduce the amount of 
ozone in the atmosphere, then before one could conclude that this would 
lead to a global cooling, it would still also have to be known if the 
clilorofluorocarbons moved the altitude of maximum ozone concen- 
tration up or down. If the maximum moved up, this would enhance 
the cooling effect of a decrease in ozone, but if the maximum moved 
down, that situation would oppose the cooling attributable to the 
decrease in total ozone. Thus, while it is conceivable that a large change 
in ozone could significantly affect climate, it may be seen that the 
direction of any potential ozone-climatic effect is difficult to deter- 
mine. 66 


Another man-generated pollutant that could affect the climate is 
waste heat generated by combustion, automobiles, home heating, in- 
dustrial processes, and power generation — all produce heat that even- 
tually is emitted into the atmosphere. In addition to its direct effect 
on atmospheric temperature, in specific situations waste heat can en- 
hance convection, the vertical motion so important in precipitation 

On a regional scale, thermal effects may become important by the 
turn of the century. However, on a global scale, climatic effects of 
thermal pollution today and for the near future appear to be insig- 
nificant. Some scientists, however, believe this impact may grow with 
increased energy production and conversion. Research meteorologist 
James T. Peterson of the Environmental Protection Agency states 
that a long-term view reveals that continued growth of energy use 
could lead to a large-scale climatic change in 100 years or more. Of 
particular concern, says Peterson, are present-day nuclear power- 
plants, which will produce about 55 percent more waste heat than a 
fossil fuel plant for a given amount of electricity generated. 67 

To better understand the effects of heat releases on weather and 
climate, the U.S. Department of Energy is sponsoring a program called 
METER, which stands for "meteorological effects of thermal energy 
releases." METER program scientists are collecting data from several 
powerplant sites around the United States to aid in predicting the 
specific environmental effects of releasing large amounts of excess heat 
and moisture directly into the atmosphere from powerplant operations 
and cooling towers. The amounts of heat and moisture emitted from 
the stacks and towers of a large powerplant are small compared with 
those released by even a moderate-sized thunderstorm. Cooling tower 
plumes are suspected of acting as a triggering mechanism to create 
instabilities in the atmosphere, initiating or otherwise modifying 
rainfall and disrupting storm patterns. A typical cooling tower will 
produce 5,000 megawatts of heat and evaporate 40,000 to 60,000 
gallons of water per minute. Even so, a modest thunderstorm will put 
out 800 times that much water and 30 times that much heat. 68 

The urban "heat island" 

• On a local scale, the climatic effects of energy use and heat produc- 
tion are significant and well documented. Obviously, urban areas are 

66 Schneider. Stephen H., "The Genesis Strategy: Climate and Global Survival." New 
York. Plenum Press, 1976. p. 183. 

67 Peterson, James T., "Energy and the Weather," Environment, vol. 15, October 1973, 
PP. 4, 5, 8. 

88 "Power Plant May Alter Weather," the Christian Science Monitor, Mar. 13, 1978, p. 19. 


experiencing thermal effects. The most evident feature of city climate 
is its excess warmth, which is commonly referred to as the urban heat 
island. Cities are prodigious sources of heat. Factory smokestacks, air- 
conditioners and heating systems of offices and homes, vehicle engines 
and exhausts — all contribute waste heat to the outside atmosphere', 
particularly in winter. Summer temperatures in the city are 0.6° C to 
1.1° C higher than in nearby rural areas, and 1.1° C to 2.2° C higher in 
winter. Also, the building materials of brick, asphalt, mortar, and 
concrete readily absorb and store more heat from the Sun than the soil 
and vegetation of a rural area, and give it up more slowly after sun- 
down. While rural areas are rapidly cooling after sunset, the building 
materials gradually release their stored heat to the urban atmosphere, 
tending to keep it warmer than the countryside. 

Another factor that retains high temperatures and makes the atmos- 
phere dry is the way a city disposes of its rainwater or snow. During 
any shower or storm, the water is quickly drained from the roofs by 
gutters and drainpipes, and from the sidewalks and streets by gutters 
and storm sewers. The winter snows are removed as quickly as possible 
by shovels and plows, and often hauled away in trucks. These methods 
of removing precipitation not only take away sources of moisture but 
also remove the cooling effect of evaporation. In the country, evapora- 
tion can cool the area where the rain and melting snow stay on the 
surface or seep into the ground. A large fraction of the absorbed heat 
energy is used in evapotranspiration as vegetation transpires water 

An advantage of urban heat emissions is that the} 7 decrease the 
likelihood of surface-based air temperature inversions (air tempera- 
ture increases rather than decreases with height) and increase the 
height of the mixed layer near the surface. Inversions inhibit turbu- 
lent air motions which diffuse and dilute pollutants. Heat emissions at 
the city surface create a relative decrease in temperature with height 
which in turn aids the mixing and dispersion of pollutants. Observa- 
tions of urban and rural temperature-height profiles have shown this 
effect of thermal emissions. Thus, urban pollutants emitted near 
ground level, such as carbon monoxide from auto exhaust, will be 
diffused through a greater volume of the atmosphere with a consequent 
reduction in concentration. 

Other major features of urban climates that are related to thermal 
pollution include : 

A longer frost-free growing season. 

Less snowfall because snow melts while falling through the 
warmer urban atmosphere and less snow accumulation because 
-now melts on contact with warmer urban surfaces. 

Lower relative humidity. 

Decreased occurrence and density of fog because of the lower 
relative humidity, a feature which may be offset by more par- 
t Iculate matter which serves as condensation nuclei. 

A slight component of the wind direction toward the city cen- 
ter as a result of the horizontal temperature contrast. 

Apparent enhancement of precipitation downwind of cities, a 
phenomenon partially due to increased convection (vertical 



The calbedo is a numerical indication of the percentage of incoming 
i>lar radiation that is reflected by the land, ocean, and atmosphere back 
into space and, attendantly, how much is absorbed by the climatic sys- 
tem. Another important manner for altering the Earth's heat budget, 
albedo can be changed by the process of urbanization, agricultural 
activities, changes in the character of the land surface, and by in- 
creasing or decreasing cloudiness. 69 

Most clouds are both excellent absorbers of infrared radiation and 
rellectors of solar radiation. Therefore, clouds are a major factor in 
determining the Earth's energy balance. An increase in clouds could 
warm surface temperatures by tending to reduce the flux of long- wave 
(that is, infrared) radiation to space, or cool surface temperatures by 
reflecting incoming solar radiation back to space. The net effect of 
increased cloudiness is to either warm or cool the surface, depending 
on cloud type, latitude, and season. 70 The effect of cloud condensation 
nuclei (CCN) on the formation of fog and clouds could alter the albedo 
of a region if the fog or clouds were sufficiently persistent or extensive, 
P. V. Hobbs and H. Harrison, both professors of atmospheric science 
at the University of Washington, and E. Eobinson of Washington 
State Universit3 T? s Air Pollution Research Unit, contend that perhaps 
the most sensitive atmospheric processes which can be affected by air 
pollutants are those involved in the development of clouds and pre- 

Apart from effects on precipitation processes, inadvertent modifi- 
cation of the microstrncture and distribution of clouds, with attend- 
ant consequences for radiative properties, could have profound effects 
on atmospheric temperature distributions and global climate. 71 
Whether a variation in terrain on temperature or other factors would 
have a negative or positive feedback interaction with clouds is a 
major question in climate theory that will be answered by extensive 
analyses of observations and model studies. 

The high reflectivity of snow and ice, as compared with water or 
land surfaces, provides positive feedback if the average year-round 
temperature decreases and the extent of ice and snow coverage in- 
creases and reflects more of the incoming sunlight back to space. The 
result is to lower the rate of heating still more, particularly in the 
regions closest to the poles. Columbia University scientists observed 
from a study of satellite photomaps that snow and icepack cover 
were more extensive and of longer duration in the early 1970's than 
in previous years. The result, they reported, was to increase the 
Earth's albedo, reflect more sunlight back into space, and change the 
planet's heat balance. 72 It was pointed out that normally vegetated 
ground reflects about 15 percent to 20 percent of sunlight and a calm 
ocean reflects 5 percent to 10 percent, while snow-covered grassland 
or pack ice reflects about 80 percent. 

88 Otterman. J., "Anthropogenic Impact on the Albedo of the Earth," Climatic Change, 
vol. 1, Xo. 2, 1977, pp. 137-155. 

70 "Living With Climatic Change," proceedings of a conference/workshop held in Toronto, 
Not. 17-22, 1975 ; Ottawa, Science Council of Canada, 1976, p. 88. 

71 Hobbs, P. V., H. Harrison, and E. Robinson, "Atmospheric Effects of Pollutants," pp. 
910, 911. 

72 The atmosphere is principally heated by terrestrial reradiation, thus the reflected 
incoming light, escaping back into space instead of being transformed into heat, represents 
a deficit in the Earth's energy balance. 


They also found that snow and ice covered twice as much ground 
in October 1972 as in October 1968 and correlated that situation with 
a drop in global air temperatures. They warned that the potential 
for fast changes of climate evidently does exist and should be kepfe 
in mind. 73 

There's yet another contributor to the planet's albedo : airborne par- 
ticles, particularly the extremely fine dust particles that have been 
carried too high in the atmosphere to be scavenged and washed out 
by precipitation processes. Many of these particles remain aloft for 
months or years. Dust of various kinds may initiate short-term cool- 
ing trends with characteristic time spans of decades or centuries. This 
depends on the optical properties of the particles, which in turn de- 
pend on particle composition and size distribution. Furthermore, par- 
ticles radiate in the infrared, and therefore can alter the outgoing 
long-wave radiation. 

Densely populated regions tend to have higher albedos than do 
forests or cultivated soils. The deserts of the world have a highei 
albedo than, for example, grass-covered fields. Urbanization, agricul- 
ture, transportation networks — all act to alter the surface albedo. 
While local changes in albedo have been determined, however, the 
overall integrated global variation is still unknown. Even local net 
effects of surface changes may not be fully understood, since changes 
in the nature of a surface are generally accompanied by change in 
surface roughness. Surface roughness alterations can affect the man- 
ner and rate of heat and momentum exchanges with the atmosphere 
through modification of small-scale turbulent processes. 74 

A factor such as roughness of the ocean should not be overlooked 
in ocean/atmosphere exchange mechanisms. Ocean surface pollution 
may also figure in the alteration of the albedo as well as the sea surface 
characteristics: an oil slick forming a surface film on the sea. for 


Beginning in the 1940's, large areas of the Texas Panhandle, western 
Oklahoma, Kansas, and Nebraska came under widespread irrigation. 
This large-scale irrigation adds more moisture to the air through 
evaporation; has made large land surfaces greener (which changes 
the albedo) ; and may act to decrease dust in the air. Since the situation 
is somewhat analogous to a large-area rain modification project, a 
number of studies have been conducted to ascertain if greater rainfall 
could occur in the vicinity or downwind of irrigated areas. 

Schickedanz (1976) provided strong evidence of irrigation-related 
anomalies; specifically, increased rainfall during months when irri- 
gation took place in and/or surrounding large irrigated areas of the 
Groat Plains. 

The percent rain increase associated with the irrigation effect was 
found to vary from 14 percent to 26 percent in June, 57 percent to 
91 percent in July, 15 percent to 26 percent in August, and 19 percent 

73 Kukla, George .T., and Helena J. Kukla, "Increased Surface Albedo in the Northern 
Hemisphere," Science, vol. 183, Feb. 22, 1974, pp. 709, 713, 714. 

A growing fraction of current evidence seems to suggest, however, that this has not been 
the in North America. Analysis of satellite data for the last decade has led scientists 
with the National Environmental Satellite Service to conclude that North American anow 
cover showed no significant change during the entire period of record. Rather, the North 
American total winter snow cover appears to be remarkably similar year to year. Eurasion 
snow cover on the other hand was reported to be much more variable. 

w National Research Council, Committee on Atmospheric Sciences, "Weather and 
Climate Modification : Problems and Progress," p. 156. 


] to 35 percent during summer depending on the location and size of 
the irrigated areas in the States of Kansas, Nebraska, Oklahoma, and 

Acting similarly to the manner in which urban industrial centers 
affect weather in and downwind of them, irrigated areas may be said 
to be a focal point for both rain initiation and rain enhancement or 
redistribution, under conditions when rain is likely. 75 ' 76 

Stick! (1975) also found evidence of irrigation-related rainfall 
, anomalies in the Columbia Basin of Washington. Explaining that the 
increase in rainfall is real, he offered the following explanation : 

The moisture added by irrigation is evaporated and must eventually return 
I to the Earth's surface as precipitation. The question is where and when? The 
[Columbia] basin is nearly surrounded by mountains. The surface layer of air 
in the basin will eventually be carried over the mountains [at the eastern margin 
of the basin], and if additional moisture has been added to the air * * * air, we 
would expect additional precipitation in the foothills. This appears to be what 
happens during the two months [of July and August] when additional evapora- 
tion is greatest. 77 


In review, tables 2, 3, and 4 summarize much of the pertinent infor- 
mation presented in the preceding sections. They are, respectively, 
"Inadvertent Effects on Ten Weather Phenomena," "Chronic Low- 
Level Pollutants : Mankind's Leverage Points on Climate," and "Pos- 
sible Causal Factors in Future Climatic Change to the Year 2000 A.D." 



Certainty of inad- Scale of inadvertent cance of inadvert- 
Phenomenon vertent effect effect ent effect 

1. Visibility and haze 







2. Solar radiation and sunshine 




3. Cloudiness 






4. Precipitation (quantity). 





Meso or macro 


Precipitation (quality).. 










5. Thunderstorms (hail/heavy rain) 







6. Severe storms (tornados, other) 




7. Temperature 





Populated meso 


8. Wind/circulation. 






9. Fog 



10. Humidity 





i From "Final Report to the National Science Foundation on the Third Inadvertent Weather Modification Workshop,'! 
Hartford, Conn., May 23-27, 1977. Hartford. The Center for Environment and Man, Inc., 1977. 

Note.— Micro: less than or equal to 1 km; urban: less than or equal to 30 km; meso: 30 to 150 km; macro: greater than 
150 km. 

75 Schickedanz, Paul T.. The Effect of Irrigation on Precipitation In the Great Plains. 
Final report on an investigation of potential alterations in summer rainfall associated 
with widespread irrigation in the Great Plains, Urbana, 111., Illinois State Water Survey, 

1976. 105 pp. 

76 Schickendanz, Paul T., "Extra-Area Effects from Inadvertent Weather Modification." 
In preprints of Sixth Conference on Planned and Inadvertent Weather Modification, 
Champaign-Urbana, 111., Oct. 10-13, 1977. Boston, American Meteorological Society, 

1977, pp. 134-137. 

"Stidd, Charles K., "Irrigation Increases Rainfall?" Science, vol. 188, Apr. 18, 1975, 
pp. 279-281. In Effect of Large-Scale Irrigation on Climate in the Columbia Basin, 
Science, vol. 184, Apr. 12, 1974, pp. 121-127. Fowler and Helvey argue that small scale 
site changes may occur, but the widespread climatic effects of irrigation may well be 
minimal. Furthermore, they contend that the available precipitation records for the 
basin do not verify Stidd's conclusion that precipitation increased because of irrigation. 




Tssues in Inadvertent Weather and Climate Modification 
climatic barriers to long-term energy growth 
Revelle and Suess (1957) stated: 

Human beings are now carrying out a large scale geophysical experiment of 
a kind that could not have happened in the past nor be repeated in the future. 
Within a few centuries we are returning to the atmosphere and ocean the con- 
centrated organic carbon stored in the sedimentary rocks over hundreds of mil- 
lions of years. This experiment may yield a far-reaching insight into the processes 
of determining weather and climate. 78 

Thus stated is the case for diligent observation of the consequences 
of the man-generated flux of carbon dioxide to the atmosphere. Left 
unstated is perhaps the greater need to anticipate the consequences 
well enough to keep them within acceptable limits. 

Even though carbon dioxide makes up a small fraction (less than 
one one-thousandth of the total atmospheric mass) of the gases that 
comprise the atmosphere, it is crucial in determining the Earth's 
temperature because it traps some of the Earth's heat to produce the 
so-called greenhouse effect. 

Worldwide industrial civilization may face a major decision over 
the next few decades — whether to continue reliance on fossil fuels as 
principal sources of energy or to invest the research and engineering 
effort, and the capital, that will make it possible to substitute other 
energy sources for fossil fuels within the next 50 years. The second 
alternative presents many difficulties, but the possible climatic con- 
sequences of reliance on fossil fuels for another one or two centuries 
may be critical enough as to leave no other choice. 

The climatic questions center around the increase in atmospheric 
carbon dioxide that might result from continuing and increasing use 
of fossil fuels. In 110 years since about 1860 a 12-percen.t increase in 
the concentration of carbon dioxide had taken place, but because of 
the exponential nature of the consumption of energy and the burning 
of fossil fuels the next 10-12 percent increase would take only about 
20 years and the next 10-12 percent increase beyond that only about 
10 years. By this time the climatic impact of the carbon dioxide should 
(according to model calculations) cause a climatic warming of about 
1°C (1.8°F). Four questions are crucial : 

1. What concentrations of carbon dioxide can be expected in the 
atmosphere at different times in the future, for given rates of combus- 
tion of fossil fuels ? 

2. What climatic changes might result from increased atmospheric 
carbon dioxide? 

3. What would be the consequences of such climatic changes for 
human societies and for the natural environment ? 

4. "What, if any, countervailing human actions could diminish the 
climatic changes or mitigate their consequences ? 79 

Whether such a warming would influence the extent of ice and snow 
at the polar caps or influence the level of the world ocean cannot be 

■« Rpvelle R. and H. E. Suess, "Carbon Dioxide Exchange Between the Atmosphere 
and Ocean,'' and the "Question of an Increase in Atmospheric Carbon Dioxide During 
the Past Decades," Tellus. vol. 9, No. 1, 1957, p. 18. . „ 

n National Research Council, Geophysics Research Board, "Energy and Climare, p. 1. 


said with certainty. Neither can it be said whether such a warming 
would push the grain belts of the world poleward by several hundred 
kilometers thereby disrupting the present patterns of agriculture. 
These are possibilities, but climatic theory is yet too crude to be certain. 
The only certain proof that the carbon dioxide-greenhouse theory is 
correct will come when the atmosphere itself ''performs the experi- 
ment" of proving present estimates too high, or too low. An important 
point remains, though, and that is : The uncertainty in present scien- 
tific estimates of potential climatic consequences of increased energy 
use is not biased toward optimism. 80 

Carbon dioxide is not the only byproduct of the burning of fossil 
fuels. Another form of atmospheric pollution results from the intro- 
duction of dust and smoke particles, which, when suspended in air. are 
called atmospheric aerosols. The word "aerosols" is a term used to 
describe the suspension of any kind of particle in a gas. These particles 
can be solid like dust, sand. ice. and soot. Or they can be droplets like 
the water particles in clouds and fog or the liquid chemicals that are 
dispensed as droplets from aerosol spray cans. The air contains tril- 
lions upon trillions of aerosol particles, which, like carbon dioxide, 
comprise only a minute fraction of the total atmospheric mass. 

Despite their relatively small volume, aerosols can affect the climate, 
primarily by absorbing and scattering back to space some of the sun- 
light that could have otherwise reached the Eartlrs surface. Industry 
is not the only human activity that causes aerosols. They are also pro- 
duced in great quantities by a variety of agricultural activities and 
practices, and a significant fraction of the particle loading of the 
atmosphere is of natural origin. 

A consensus among scientists today would not be forthcoming as to 
whether an increase in aerosols would result in a cooling of the climat < 3 
or a warming of the climate, because aerosols will cool the climate if 
they are relatively whiter than the surface over which they lie, or, 
alternatively, they will warm the Earth if they are relatively darker 
than the surface over which they are suspended. The dust that exists in 
the atmosphere today is highly nonuniform in both geographic distri- 
bution and relative brightness as compared to the underlying surface. 
Therefore, one cannot be absolutely certain whether dust contributes 
to climatic warming or can be implicated in climatic cooling. sl 



Putting together the different parts of the story of climate and 
energy, what picture emerges? How seriously do we respond to the 
possibility that the present rate of increase of fossil fuel burning is 
likely to have noticeable consequences for climate by the end of this 
century, but not become a serious problem until well into the next 
century? On the longer time scale, the picture that emerges is rather 
startling in the words of Dr. Wallace Broecker of the Lamont-Doherty 
Geological Observatory, who explains, "Consumption of the bulk of 
the world's known fossil fuel reserves would plunge our planet into a 

80 Schneider, Stephen H., "Climate Change and the World Predicament." Climatic 
Change, vol. 1, No. 1, March 1977, pp. 31-33. 
61 Ibid., pp. 34, 35. 


superinterglacial, the likes of which the world lias not experienced in 
the last million years." 82 

Admittedly, we are talking here of possibilities, not certainties. The 
climatic consequences of massive fossil fuel consumption may be less 
severe than assessments project, but they might be more severe. Man- 
kind eventually may discover a new energy source that will obviate the 
need to use fossil reserves so extensively for that purpose, and yet a 
fossil-fuel-free world in the relatively near future is so bizarre an idea 
it is hard even to talk about it seriously. Or perhaps technology could 
develop a cosmetic, such as the introduction of an artificial dust layer 
surrounding the Earth to screen some of the incoming sunlight. This 
could tend to offset the warming effect of the added carbon dioxide. 

What would happen if society elected to ignore the problem of 
carbon dioxide until it manifested itself (perhaps in another 20 years) 
in the form of a clear signal that a global warming trend had begun 
that was unmistakably attributable to the further accumulation of 
carbon dioxide in the atmosphere? Delaying until then a mandated 
action to phase over the principal energy sources from fossil fuels to 
other alternative kinds of fuels and taking into account another 
several decades for the transition to be completed would put us half- 
way into the next century before the problem could be shut off at its 
source. But perhaps the most disturbing aspect of the carbon dioxide 
problem is that the effects of carbon dioxide would endure for hundreds 
of years, even after the abandonment of the fossil fuel economy, because 
of the long recovery time associated with the processes that would rid 
the atmosphere of excess carbon dioxide and establish an equilibrium 

This carbon dioxide Sword of Damocles, if indeed it exists, implies 
development of solar (including wind, ocean, biomass, etc.) fisson, 
fusion, and geothermal at a somewhat more rapid pace than is gen- 
erally recognized. 83 

Asserts J. Murray Mitchell, Jr. : 

The alternative is clear. Ours is the generation that must come to grips with 
the carbon dixoide problem and mount a vigorous research effort to allow us to 
understand all of its ramifications for the future. Ours is the generation that may 
have to act, and act courageously, to phase out our accustomed reliance on fossil 
fuels before we have all the knowledge that we would like to have to feel that 
such action is absolutely necessary. * * * We can scarcely afford to leave the 
carbon dioxide problem to the next generation. 84 


Despite everything that science has learned about the broad charac- 
teristics of climate and climatic history, relatively little is known of 
the major processes of climatic change. Lack of knowledge still is a 

82 Mitchell, J. Murray^ Jr., "Carbon Dioxide and Future Climate," p. 9. 

83 Rotty, R. M. and A. M. Weinherg, "How Long Is Coal's Future," pp. o5-57. 
M Mitchell, J. Murray, Jr., "Carbon Dioxide and Future Climate," p. 9. 


major barrier to accurate forecasting and understanding of potential 
inadvertent modification of weather and climate. The atmosphere and 
the ocean make up such a complex and rapidly changing system that 
even short-range forecasts may often be incorrect. Gathering sufficient 
information about global climate is of importance if atmospheric 
scientists are to construct the detailed computerized models capable of 
rapidly analyzing enormous amounts of data concerning each com- 
ponent of the climatic system, which includes not only the atmosphere 
but the world ocean, the ice masses, and the exposed land surface. 

Observations are essential to the development of an understanding 
of climatic change. Without them, theories will remain theories and 
models would be of limited usefulness. Observational records need to 
be extended in both time and space to facilitate adequate documenta- 
tion of the climatic events that have occurred in the past and monitor- 
ing of the climatically important physical processes occurring now. 

Knowledge of the mechanisms of climatic change may be at least as 
fragmentary as the state of the data. Not only are the basic scientific 
questions largely unanswered, but in many cases not even enough is 
known to pose the key questions. What are the most important causes 
of natural climatic variation, and which are the most important or 
most sensitive of the many processes involved in the interaction of the 
air, sea, ice, and land components of the climatic system ? There is no 
doubt that the Earth's climates have changed in the past and will likely 
change in the future. But will it be possible to recognize the first phases 
of a truly significant climatic change when it does occur ? 

In a 1975 report, "Understanding Climate Change : A Program for 
Action/' the U.S. Committee for the Global Atmospheric Research 
Program of the Xational Research Council enumerated the principal 
approaches to these problems emphasizing the interdependence of the 
major components of a climatic research program and posing a number 
of key questions. The components included : 

Climatic data analysis : What has happened in the past? 

Empirical studies : How does the system work? 

Monitoring : What is going on now ? 

Numerical models: What is shown by climatic simulations? 

Theoretical studies : How much do we really understand ? 

Climatic impacts : What does it all mean to man ? 

Future climates : How and when is the climate going to change ? 
The various components of the climatic research program are to a 
great extent interdependent : Data are needed to check general circula- 
tion models and to calibrate the simpler models ; the models are needed 
to test hypotheses and to project future climates : monitoring is needed 
to check the projections ; and all are needed to assess the consequences. 85 

85 National Research Council, U.S. Committee for the Global Atmospheric Research 
Program. "Understanding Climatic Change : A Program for Action," Washington, National 
Acadmy of Sciences, 1975, pp. 5, 6. 



Effort Frequency 

variable or index Method Coverage required • required 2 

Atmospheric indices: 

Solar constant Satellite Global N W 

Absorbed radiation, albedo do do P W 

Latent heating... do. N W 

Surface latent heat flux do World ocean N W 

Surface sensible heat flux do Regional N W 

Cloudiness do Global P W 

Surface wind over ocean Radar scattering World ocean N W 

Oceanic indices: 

Sea-surface temperature Ships, satellites, buoys... World ocean E W 

Surface-layer heat storage XBT, AXBT, buoys Mid-latitude and low- E, N W 

latitude oceans. 

Heat transport Moored buoys Selected sections N W 

Temperature structure .Ships do E S 

Surface salinity Ships, buoys. High latitudes E W 

Sea level .1 Tide gauges Selected coastal and E W 

island sites. 

Composition, dissolved gases Conventional sampling. Selected sections E S 

Cryospheric indices: 

Floating ice extent Satellite Polar seas, lakes E M 

Ice-sheet budget parameters do Greenland, Antarctica N Y 

Mountain glacier extent do Selected sites E Y 

Snow cover. do Continents E M 

Surface and hydrologic indices: 

River discharge Flow gauges Selected sites E, N W 

Soil moisture Satellite Land areas E W 

Lake levels Gauges Selected sites E W 

Precipitation Satellite, radar, gauges... Global E W 

Composition and turbidity indices: 

Chemical composition Sampling Selected sites E S 

Aerosols and dust Satellite Global. E W 

Anthropogenic indices: 

Thermal pollution Sampling.. Continents and coasts N W 

Air and water pollution do Global.. E W 

Land use Satellite Continents E Y 

1 N, completely new monitoring effort required; E, expansion of present monitoring efforts required; P, present (or 
slightly expanded) monitoring efforts satisfactory but coordination and further analysis required, 
a W, weekly (or possibly daily in some cases); M, monthly; S, seasonally; Y, yearly (or possibly decadal in some cases). 

Source: Natichal Research Council, U.S. Committee for the Global Atmospheric Research Program, "Understanding 
Climatic Change: A Program for Action," Washington, National Academy of Sciences, 1975; pp. 78-79. 

The Committee on Atmospheric Sciences, also of the National Re- 
search Council, stated in a 1973 report entitled "Weather and Climate 
Modification : Problems and Progress" that if society is to deal with 
long-term problems of inadvertent weather modification and climatic 
changes caused by man and his activities, then urgent attention and 
action are required at the earliest possible moment. The Committee 
outlined several courses of action that should be undertaken, each con- 
tributing to a part of the necessary work to be accomplished: 

1. A worldwide network of ground-based stations is needed to moni- 
tor the properties of the atmosphere with particular attention being 
given to those gases and aerosols affecting radiation and heat transfer. 
Precipitation collection should be undertaken for the analysis of 
atmospheric chemical constituents. Surface monitoring efforts should 
also be augmented by airborne monitoring of particles and gases in the 
atmosphere. Table 5 summarizes in detail the variables to be moni- 
tored, the method of monitoring, coverage, effort required and fre- 
quency required. 

2. Since influence on climate caused by human factors is a global 
matter, internationally cooperative plans should be established that 
will provide long-term and uniform monitoring data. 


3. Continuous monitoring of the Earth by satellites should be devel- 
oped to measure not only cloud cover and cloud types but also the ther- 
mal characteristics of the atmosphere and the Earth's surface, as well 
as related variations in the albedo of the Earth. Satellite measurements 
should be complemented by a program of ground-based remote sensing 
of the dynamical, chemical, and particulate properties of the 

4. Computer capabilities for simulation of climate and climatic 
changes should be fully utilized. Climatic models eventually may prove 
to be quite different from the present general circulation models. How- 
ever, if we are to reach the capability to assess the consequences of 
further human intervention, climatic model development must be 
promptly undertaken. 86 

Many of the efforts envisaged are of an obvious international charac- 
ter, and the degree to which they should be regarded as national versus 
international activities is not of critical importance. The important 
point is, however, that there are international efforts now underway of 
drect relevance to the climatic problem. 

The World Meteorological Organization (WMO) and the Interna- 
tional Council of Scientific Unions (ICSU) jointly organized a global 
atmospheric research program (GARP) in 1967. GARP goals in- 
clude : providing the improved understanding of the global circulation 
needed to extend the range and accuracy of weather forecasts; under- 
standing the physical basis of climate and climatic fluctuations ; and 
providing a firm foundation for the World Weather Watch 
(WWW). 87 

Several GARP regional expirements are planned in order to exam- 
ine specific processes. Hie GARP Atlantic Tropical Experiment 
(GATE) followed the Barbados Oceanographic and Meteorological 
Experiment (BOMEX, 1969) in a succession of experiments designed 
to gain increased understanding of the atmosphere and the causes of 
climatic variation and change. The primary objective of GATE was 
to learn more about the meteorology of the tropical equatorial belt 
where vast quantities of heat and moisture, carried upward by orga- 
nized convective systems, are transported and redistributed to higher 
latitudes, ultimately affecting global atmospheric circulation patterns. 
Because the tropics are believed to be a key to these circulation pat- 
terns, scientists expect data from GATE to help them better under- 
stand the global climate machine. Conducted as scheduled from June 15 
to September 30, 1974, GATE had the cooperation of some 72 coun- 
tries. In addition to BOMEX and GATE, experiments designed to 
contribute to the understanding of specific oceanic-atmospheric proc- 
esses in selected regions are : the Air Mass Transformation Experiment 
( AMTEX) , the Monsoon Experiment (MONEX) , and the Polar Ex- 
periment (POLEX). These regional experiments and the knowledge 
gleaned from them will culminate in a truly international global ob- 
serving experiment, the First GARP Global Experiment (FGGE) 
scheduled for the late 1978-79 timeframe. 

86 National Research Council. Committee on Atmospheric Sciences, 'Weather and Climate 
Modification : Problems and Progress," pp. 160, 161. 

87 WWW is an operational program of member nations of the WMO for making available 
the basic meteorological and related environmental information needed by each member 
aation to supplement and support Its meteorological services and research. 

34-857—79 15 


The program goals of GARP intersect with the objectives of other 
international environmental programs. One such program is the Inter- 
governmental Oceanographic Commission Integrated Global Ocean 
Station System (IGOSS) being developed jointly with the World 
Meteorological Organization to provide more extensive and timely 
information for analysis and prediction of the state of the oceans and 
for research purposes. This is accomplished through the development 
of a comprehensive monitoring system for the total physical ocean- 
atmosphere environment. Another is EARTH WATCH, a major com- 
ponent of the United Nations Enviornment Program (UNEP) being 
developed to monitor and assess the state of the oceans, atmosphere, 
land and human health in order that rational decisions can be made 
for the management of the environment. EARTHWATCH will also 
interact with and depend on the monitoring and research capabilities 
of GARP. A key component of the UNEP/EARTHWATCH global 
baseline and regional monitoring effort is the Global Environment 
Monitoring System, which is designed to measure and monitor 
priority pollutants and related factors of the atmospheric environ- 
ment, thus permitting quantitative assessment of the global impact 
of manmade and natural influences on weather and climate. 

The Global Observing System provides worldwide meteorological 
and related environment observation data needed by the World 
Weather Watch and GARP. The overall system consists of two subsys- 
tem? : a space-based satellite subsystem, composed of two types of 
satellites, those in polar orbit and those in geostationary orbit; and a 
surf ace-based subsystem composed of basic synoptic surface and upper 
air networks, other networks of stations on land and sea, and aircraft 
meteorological observations. 

The U.S. Committee for the Global Atmospheric Research Program 
believes that these observational programs planned in support of 
GARP offer an unparalleled opportunity to observe the global atmos- 
phere, and furthermore that every effort should be made to use these 
data for climatic purposes as well as for the purposes of weather pre- 
diction. The Committee emphasized however, that the climatic system 
consists of important nonatmospheric components, including the 
world's oceans, ice masses, and land surfaces, together with elements 
of the biosphere. While it is not necessary to measure all of these com- 
ponents in the same detail with which the atmosphere is observed, 
their roles in climatic variation should not be overlooked. 88 

The Committee's 1975 report, "Understanding Climatic Change: 
A Program for Action," further stated that : 

The problem of climatic variation differs from that of weather forecasting by 
the nature of the data sets required. The primary data needs of weather predic- 
tion are accurate and dense synoptic observations of the atmosphere's present 
and future states, while the data needed for studies of climatic variation are 
longer-term statistics of a much wider variety of variables. When climatic varia- 
tions over long time scales are considered, these variables must be supplied from 
fields outside of observational meteorology. Thus, an essential characteristic of 
climate is its involvement of a wide range of nonatmospheric scientific disciplines, 
for example, oceanography, glaciology, hydrology, astronomy, geology, and 
paleantology as well as from the biological and social sciences of ecology, geog- 
raphy, archaeology, history, economics, and sociology. 

88 N'.-itionnl Research Council, U.S. Committee for the Global Atmospheric Research 
Program, "Understanding Climatic Change: A Program for Action," pp. 105, 106. 


The types of numerical models needed for climatic research also differ from 
those of weather prediction. The atmospheric general circulation models do not 
need a time-dependent ocean for weather-forecasting purposes over periods of a 
week or two. For climatic change purposes, on the other hand, such numerical 
models must include the changes of oceanic heat storage. Such a slowly varying 
feature may be regarded as a boundary or external condition for weather predic- 
tion but becomes an internal part of the system for climatic variation. 89 

In view of these characteristics, the Committee suggested that while 
the GARP concern with climate was a natural one, the problem of 
climate goes much beyond the present basis and emphasis of GARP. 
Accordingly, they recommended that the global climate studies that 
are under way within GARP be viewed as leading to the organization 
of a new and long-term international program devoted specifically to 
the study of climate and climatic variation, an international climatic 
research program (ICRP). 

As viewed by the Committee the main thrust of the international 
climatic program would be the collection and analysis of climatic data 
during a series of international climatic decades (ICD) designated for 
the period 19S0-2000. During this period, the cooperation of all nations 
would be sought to participate in an intensive effort to develop and 
secure as complete a global climatic data base as possible. The Com- 
mittee urged the creation of an international cooperative program for 
the monitoring of selected climatic indices and the extraction of his- 
torical and proxy climatic data unique to each nation, which would 
include, but not be limited to, such indices as glaciers, rain forest pre- 
cipitation, lake levels, local desert history, tree rings, and soil records. 
This would take the form of an international paleoclimatic data net- 
work (IPDX) , as a subprogram of the ICRP. 

To promote wider international participation in climatic research, 
it was recommended that programs and activities be developed to 
encourage international cooperation in climatic research and to facili- 
tate the participation of developing nations that do not yet have ade- 
quate training or research facilities. Internationally supported re- 
gional climatic studies describing and modeling local climatic anom- 
alies of special interest were also recommended. 90 

The Committee stressed the importance of international cooperative 
programs to assess the impacts of presently observed climatic changes 
on the economies of the world's nations, including the effects on water 
supply, food production, and energy utilization, as well as analyses of 
the regional impacts of possible future climates. 

IMd., p. 106. 

00 The World Meteorological Organization headquarters in Geneva is planning a world 
conference on climate, tentatively to be held in 1979. 



(By Robert E. Morrison, Specialist in Earth Sciences, Science Policy Research 
Division, Congressional Research Service) 

Overview of Federal Activities 

The Federal Government has been involved for over 30 years in a 
number of aspects of weather modification, through activities of both 
the Congress and the executive branch. Since 1947, weather modifica- 
tion bills pertaining to research support, operations, policy studies, 
regulations, liabilities, activity reporting, establishment of panels and 
committees, and international concerns have been introduced in the 
Congress. There have been hearings on many of these proposed meas- 
ures, and oversight hearings have also been conducted on pertinent 
ongoing programs. A total of six public laws specifically on weather 
modification have been enacted since 1953, while others have included 
provisions which in some way are relevant to weather modification. 
Resolutions dealing with the use of weather modification technology 
as a weapon by U.S. military forces and promotion of a U.N. treaty 
prohibiting such activities have been introduced in both houses of the 
Congress, and one such resolution was passed by the Senate. 

Federal legislation has dealt principally with three aspects of 
weather modification — research program authorization and direction, 
collection and reporting of weather modification activities, and the 
commissioning of major studies on recommended Federal policy and 
the status of technology. In addition to providing direction through 
authorizing legislation, the Congress has initiated one major Federal 
program through an appropriations bill write-in, and this program 
has since regularly received support through additional appropria- 
tions beyond its recommended OMB funding level. 

Identifiable Federal research and operational weather modification 
programs can be traced from at least the period of World War II; 
however, the research programs of most agencies other than the De- 
fense Department were not begun until the 1950's and 1960's. "While 
these research and development programs sponsored at various times 
by at least eight departments and independent agencies have consti- 
tuted its major involvement, the executive branch has also performed 
a wide range of other weather modification activities. Such activities 
include the conduct of modest operational programs, coordination of 
Federal research programs, collection and dissemination of U.S. 
weather modification activities, sponsoring of in-depth studies, publi- 
cation of a large variety of reports, negotiation for international re- 
strictions barring hostile use of weather modification, and cooperation 
with other nations in planning of international research projects or 
assisting in foreign operational programs. The latter two activities, 



both essentially international in scope, are only noted here but are dis- 
cussed more fully in the chapter on international aspects. 1 

While some of the numerous studies on weather modification have 
been undertaken at the direction of the Congress, others have been 
initiated by one or more Federal agencies or by interagency committees 
of the executive branch. Published reports have included those which 
present the findings and recommendations of the special studies under- 
taken, those which are published periodically by agencies or commit- 
tees with regular responsibilities for reporting on Federal programs 
or on operational activities, and the many publications on specific re- 
search projects which are prepared by the individual agencies or by 
contractors and grantees participating in the respective projects. Later 
in this chapter some of the Federal reports which fall into the first two 
categories are identified under the discussions of major studies, Fed- 
eral structure, and coordination of weather modification; reports 
from the third category are referenced from time to time throughout 
the report. Some of the Federal reports are included in the selected 
bibliography in appendix H and many are also listed in the other 
major bibliographies which are referenced in that appendix. 

Legislative and Congressional Activities 
federal legislation on weather modification 


Congressional interest in weather modification has been demon- 
strated by the fact that legislation on the subject has been introduced 
in nearly every session of Congress since 1947. Nevertheless, in spite of 
the apparent interest, a total of six public laws relating specifically and 
directly to weather modification have been enacted during this period, 
and two of those passed were mere time extensions of specific provisions 
in earlier laws. 2 Briefly, these laws are : 

Public Law 83-256 (67 Stat. 559) of August 13, 1953, to create 
an Advisory Committee on Weather Control, to perform a com- 
plete study and evaluation of public and private experiments in 
weather modification to determine the U.S. role in research, opera- 
tions, and regulation ; 

Public Law 84-664 (70 Stat. 509) of July 9, 1956, to extend the 
authorized life of the Advisory Committee for 2 years through 
June 30, 1958 ; 

Public Law 85-510 (72 Stat. 353) of July 12, 1958, to authorize 
and direct the National Science Foundation to initiate a program 
of study, research, and evaluation in the field of weather modifica- 
tion and to prepare an annual report to the Congress and the 
President on weather modification ; 

Public Law 92-205 (85 Stat. 736) of December 18, 1971, to pro- 
vide for the reporting of weather modification activities to the 
Federal Government through the Secretary of Commerce and for 
dissemination of that information by the Secretary of Commerce 
from time to time ; 

1 See ch. 10. 

* Tliese six public laws are reproduced In app. I. 


Public Law 93-436 (88 Stat. 1212) of October 5, 1974, to extend 
appropriation authorization for reporting and disseminating 
weather modification activities through the Secretary of Com- 
merce, as prescribed by Public Law 92-205, through 1977; 

Public Law 94-490 (90 Stat. 2359) of October 13, 1976, to 
authorize and direct the Secretary of Commerce to develop a na- 
tional policy on weather modification and to extend appropriation 
authorization for reporting and disseminating weather modifica- 
tion activities, as prescribed by Public Law 92-205, through 1930. 
Although not exclusively concerned with weather modification, 
another act, Public Law 90^t07 of July 18, 1968, amended the National 
Science Foundation Act of 1950. Section 11 of this new act specifically 
repealed Public Law 85-510, by which the XSF had been directed to 
initiate and support a program of study, research, and evaluation in 
weather modification and to report annually on the subject. 

Another law of some significance to weather modification, though 
much broader in its overall purpose, was the fiscal year 1962 public 
works appropriation, Public Law 87-330 (75 Stat. 722) of Septem- 
ber 30, 1961. Through a $100,000 write-in to this bill, the Congress 
initiated the atmospheric water resources program (Project Sky- 
water) , conducted by the Bureau of Reclamation in the Department 
of the Interior. Through subsequent public works appropriations the 
Congress has continued to provide direction to this program almost 
every year since its inception and has provided frequent funding 
increases over levels budgeted by the administration. 

\The Advisory Committee on Weather Control 

Between 1951 and 1953 it was disclosed in congressional hearings on 
several bills introduced by both parties that water users (farmers, 
ranchers, electric utilities, and municipalities) were spending between 
$3 million and $5 million annually on weather modification and that 
such activities covered about 10 percent of the country's land area. 3 It 
was the opinion of the Congress in 1953 that "research and development 
in the field of weather modification have attained the stage at which the 
application of scientific advances in this field appears to be practical.*' 
but also that "the effect of the use of measures for the control of weather 
phenomena upon the social, economic, and political structures * * * 
and upon national security cannot now be determined. It is a field in 
which unknown factors are involved. It is reasonable to anticipate, 
however, that modification and control of weather, if effective on a 
large scale, would result in vast and far-reaching benefits to agricul- 
ture, industry, commerce, and the general welfare and common 
defense." 4 

Recognizing possible deleterious consequences which might follow 
application of weather modification techniques with inadequate safe- 
guards or incomplete understanding, and realizing that weather modi- 
fication experiments or operations could possibly affect areas extending 
across State and national boundaries, the Congress considered that such 
activities "are matters of national and international concern" and ac- 
cordingly, declared it "to be the policy of the Congress, in order to effect 
the maximum benefit which may result from experiments and opera- 

a Advisory Committee on Weather Control, final report, Washington, D.C., U.S. Govern- 
ment Printing Oflice. Dec. 31, 1957, vol. I, p. 8. 

4 Public Law S3-256 (67 Stat. 559), Aug. 13, 1953, statement of purpose and policy. 


tions designed to modify and control weather, to correlate and evaluate 
the information derived from such activity and to cooperate with the 
several States and the duly authorized officials thereof with respect to 
such activity, all to the end of encouraging intelligent experimentation 
and the beneficial development of weather modification and control, 
preventing its harmful and indiscriminate exercise, and fostering 
sound economic conditions in the public interest." 5 

In order to determine the extent to which the United States should be 
involved in weather modification research and/or operations and in the 
regulation of such activities, the Advisory Committee on Weather Con- 
trol was established by Public Law 83-256, approved August 13, 1953, 
and was directed by that law to make a complete study and evaluation 
of public and private experiments in weather control. 

The Committee was to be composed of Government and non-Govern- 
ment members in about equal number and, in carrying out its man- 
date, was given authority to conduct hearings, to acquire pertinent 
information and records from departments and agencies of the execu- 
tive branch, and to enlist the services of personnel of any agency of 
the Federal Government (with the consent of the agency concerned). 6 
The Committee was requested to submit from time to time reports on 
its findings and recommendations to the President for submission to 
the Congress and was directed to submit its final report to the Presi- 
dent for transmittal to the Congress by June 30, 1956. 7 It became clear 
that the study was of such magnitude that additional time would be 
required for its successful completion, and the Committee requested 
that its life be extended 2 years, noting that . . it has succeeded in 
establishing some positive and important results which justify the 
Federal Government continuing its special interest in the field. " 8 
Thereupon, the Congress passed Public Law 84-664 (70 Stat. 509) 
of July 9, 1956, which extended the date for completion of the report 
until June 30, 1958. The final report of the Committee was submitted 
to the President on December 31, 1957. 9 

Direction to the National Science Foundation 

The Advisory Committee on Weather Control recognized that the 
development of weather modification rested on fundamental knowl- 
edge obtainable only through scientific research into processes in the 
atmosphere and recommended that an agency, preferably the Na- 
tional Science Foundation (XSF), be designated to promote and sup- 
port meteorological research in needed fields, to coordinate research 
projects, and to constitute a central point for assembly, evaluation, 
and dissemination of information. 10 Accordingly, when the Congress 
enacted Public Law 85-510 of July 10, 1958, which amended the Na- 
tional Science Foundation Act of 1950, additional responsibilities 
were incorporated, directing the Foundation : 

To initiate and support a program of study, research, and evaluation in the 
field of weather modification, giving particular attention to areas that have 

c Ibid. 

• Ibid., sec. 9. 

7 Ibid., sec. 10. „ tl y,. _. 

s Advisory Committee on Weather Control, first interim report, Washington. D.C., Feb- 
ruary 1956, p. ii. _ 

9 Advisory Committee on Weather Control. "Final Report of the U.S. Advisory Com- 
mittee on Weather Control," Washington, DC, U.S. Government Printing Office, March 6, 
1958, in two volumes. 32 and 422. pp. (Recommendations of the Committee are found in 
tbi< chapter, p. 2''.R. and in chapter G. ) 

:o Ibid., vol. I, pp. vii-vili. 


experienced floods, drought, hail, lightning, fog, tornadoes, hurricanes, or other 
weather phenomena, and to report annually to the President and the Congress 
thereon. 11 

The In SF was further directed to ". . . consult with meterologists 
and scientists in private life and with agencies of Government inter- 
ested in, or affected by, experimental research in the field of weather 
control." 12 Authority was given to NSF to hold hearings, to require 
the keeping of records and furnishing of information on weather 
modification research and operations, and to inspect records and 
premises as appropriate in order to carry out the responsibilities 

In effect, the NSF was asigned the "lead agency" role (a term 
which was in later years to become the subject of much debate and 
discussion) among Federal agencies involved in weather modification. 
A decade later, the Foundation was stripped of these specific respon- 
sibilities and of this lead agency role when the Congress again 
amended the National Science Foundation Act of 1950, by passing 
Public Law 90-407 of July 18, 1968. Section 11 of the 1968 law struck 
section 14 and paragraph (9), subsection (a), of section 3 from the 
National Science Foundation Act, terminating as of September 1, 1968, 
the responsibilities spelled out in these sections a decade earlier with 
regard to weather modification. 

The Senate report which accompanied the bill subsequently enacted 
as Public Law 90-407 stated that the NSF was divested of these func- 
tions ". . . for a number of reasons :" 13 

One [reason] is that the ramifications of weather modification are so broad 
as to encompass far more issues than scientific ones. Another is that progress 
in this area has reached the point where it requires much developmental work 
as well as continued research. The Departments of Commerce and Interior are 
assuming much of the responsibility in this area, which the Foundation may con- 
tinue to back up with appropriate support for some of the research still needed. 
NSF retains ample authority to continue support for the latter . . . and clearly 
should do so. The Foundation will in any case continue those research activities 
necessary to preserve continuity in the program, pending passage of the weather 
modification legislation now pending. In the latter regard, the committee calls 
attention to the necessity for legislation to continue elsewhere in the executive 
branch the development and reporting activities which NSF will not have author- 
ity to support after September 1, 1968. 

Although legislation was introduced and considered by the Congress 
which would have reassigned this lead agency role to another agency, 
no further congressional action was taken on weather modification 
until 1971. 

Reporting of weather modification activities to the Federal Govern- 

Responsibility for maintaining a depository for information on U.S. 
weather modification activities and for reporting annually on Federal 
programs and the general status of the field rested with the National 
Science Foundation for the 10-year period from 1958 through 1968, 
after which, as has been noted, these and other functions were sus- 
pended by Public Law 90-407. 

11 National Science Foundation Act of 1950. as amended by Public Law S5-510 (72 Stat' 
358) of July 11. 1958. sec. 3. subsec. fa), par. (9). 

12 Ibid., sec. 14. 

13 U.S. Congress. Senate. Committee on Labor and Public Welfare, "National Science 
Foundation — Functions — Administration." report to accompany H.R. 5404. Washington, 
U.S. Government Printing Office, 1968. (90th CoDg., 2d sess. Senate Kept. No. 1137.) 


After a lapse of over 3 years, the Congress passed Public Law 92- 
205 (85 Stat. 736) of December 18, 1971, which directed that ". . . no 
person may engage or attempt to engage in any weather modification 
activity in the United States unless he submits to the Secretary of 
Commerce such reports with respect thereto, in such form and con- 
taining such information, as the Secretary may by rule prescribe. The 
Secretary may require that such reports be submitted to him before, 
during, and after such activity or attempt." 14 The act further states 
that the Secretary of Commerce is charged with responsibility to 
maintain a record of such weather modification activities in the United 
States and to publish summaries of the activities "from time to time" 
as deemed appropriate, Such information received under the provi- 
sions of this law, with certain exceptions, is to be made fully available 
to the public. 15 Authority was provided to the Secretary to obtain the 
required information by rule, subpena, or other means and to inspect 
the records and premises of persons conducting weather modification 
projects, as necessary, to carry out assigned responsibilities. There is 
also provision for levying fines up to $10,000 on any person for non- 
compliance with the stipulations of the law requiring the reporting of 
weather modification activities. Public Law 92-205 is concerned with 
the reporting of weather modification projects, however, not with 
their regulation, control, or evaluation. 

Within the Commerce Department, the weather modification report- 
ing system required by Public Law 92-205 is administered on behalf 
of the Secretary by the National Oceanic and Atmospheric Adminis- 
tration (NOAA). Upon subsequent advertisement of Commerce De- 
partment rules in the Federal Eegister, the requirement for submitting 
information on weather modification projects became effective on 
November 1, 1972. Federal agencies were excluded from the require- 
ment to submit such information under the act; however, upon mutual 
agreement by the agencies to do so, data on Federal projects have also 
been collected and disseminated by NO A A as of November 1, 1973. 

Appropriations for administering the provisions of Public Law 
92-205 were authorized through June 30, 1974, by the original law. 
Additional authorizations for appropriations, extending the responsi- 
bility of the Secretary of Commerce for reporting procedures, were 
approved by the Congress in two subsequent laws. Public Law 93-436 
(88 Stat. 1212) of October 5, 1974, extended reporting requirements 
through June 30, 1977; while Public Law 94-490 (90 Stat. 2359) of 
October 13, 1976, contained among other provisions a similar exten- 
sion of these provisions through June 30, 1980. The major thrust of the 
latter act, known as the National Weather Modification Policy Act of 
1976. is discussed in the next section. 

The National Weather Modification Policy Act of 1976 

After consideration of a number of bills introduced in the 94th 
Congress and extensive hearings on weather modification, the Con- 
gress passed Public Law 94-490 (90 Stat. 2359) , the National Weather 
Modification Policy Act of 1976, which was signed October 13, 1976. 
The following particular findings prompted the Congress to take 
action : 

1. weather-related disasters and hazards, including drought, 
hurricanes, tornadoes, hail, lightning, fog, floods, and frost, result 

54 Public Law 92-205 (85 Stat. 73G). sec. 2. 
« Ibid., sec. 3 


in substantial human suffering and loss of life, billions of dollars 
of annual economic losses to owners of crops and other property, 
and substantial loss to the U.S. Treasury ; 

2. weather modification technology has significant potential for 
preventing, diverting, moderating, or ameliorating the adverse 
effects of such disasters and hazards and enhancing crop produc- 
tion and the availability of water; 

3. the interstate nature of climatic and related phenomena, the 
severe economic hardships experienced as the result of occasional 
drought and other adverse meteorological conditions, and the ex- 
isting role and responsibilities of the Federal Government with 
respect to disaster relief, require appropriate Federal action to 
prevent or alleviate such disasters and hazards ; and 

4. weather modification programs may have long range and 
unexpected effects on existing climatic patterns which are not 
confined by national boundaries. 16 

By this act the Congress proposed "* * * to develop a comprehensive 
and coordinated national weather modification policy and a national 
program of weather modification research and development — 

1. to determine the means by which deliberate weather modifica- 
tion can be used at the present time to decrease the adverse impact 
of weather on agriculture, economic growth, and the general pub- 
lic welfare, and to determine the potential for weather modifica- 

2. to conduct research into those scientific areas considered most 
likely to lead to practical techniques for drought prevention or 
alleviation and other forms of deliberate weather modification; 

3. to develop practical methods and devices for weather modifi- 
cation ; 

4. to make weather modification research findings available to 
interested parties ; 

5. to assess the economic, social, environmental, and legal im- 
pact of an operational weather modification program ; 

6. to develop both national and international mechanisms de- 
signed to minimize conflicts which may arise with respect to the 
peaceful uses of weather modification ; and 

7. to integrate the results of existing experience and studies in 
weather modification activities into model codes and agreements 
for regulation of domestic and international weather modification 
activities." 17 

The act charges the Secretary of Commerce with responsibility for 
conducting "a comprehensive investigation and study of the state of 
scientific knowledge concerning weather modification, the present 
state of development of weather modification technology, the problems 
impeding effective implementation of weather modification tech- 
nology, and other related matters. Such study shall include — 

(1) A review and analysis of the present and past research 
efforts to establish practical weather modification technology, 
particularly as it relates to reducing loss of life and crop and prop- 
erty destruction ; 

(2) A review and analysis of research needs in weather modifi- 
cation to establish areas in which more research could be expected 

16 Public Law 94-490 (90 Stat. 2359), sec. 2, declaration of policy. 

« Ibid. _ 


to, yield the greatest return in terms of practical weather modifi- 
cation technology ; 

(3) A review and analysis of existing studies to establish the 
probable economic importance to the United States in terms of 
agricultural production, energy, and related economic factors 
if the present weather modification technology were to be effec- 
tively implemented ; 

(4) An assessment of the legal, social, and ecological implica- 
tions of expanded and effective research and operational weather 
modification projects ; 

(5) Formation of one or more options for a model regulatory 
code for domestic weather modification activities, such code to be 
based on a review and analysis of experience and studies in this 
area, and to be adaptable to State and national needs ; 

(6) Recommendations concerning legislation desirable at all 
levels of government to implement a national weather modifica- 
tion policy and program ; 

(7) A review of the international importance and implications 
of weather modification activities by the United States ; 

(8) A review and analysis of present and past funding for 
weather modification from all sources to determine the sources 
and adequacy of funding in the light of the needs of the Nation ; 

(9) A review and analysis of the purpose, policy, methods, and 
funding of the Federal departments and agencies involved in 
weather modification and of the existing interagency coordination 
of weather modification research efforts ; 

(10) A review and analysis of the necessity and feasibility of 
negotiating an international agreement concerning the peaceful 
uses of weather modification ; and 

(11) Formulation of one or more options for a model interna- 
tional agreement concerning the peaceful uses of weather modifi- 
cation and the regulation of national weather modification-activ- 
ities ; and a review and analysis of the necessity and feasibility of 
negotiating such an agreement. 18 

The act directs each department and agency of the Federal Gov- 
ernment to furnish pertinent information to the Secretary of Com- 
merce and authorizes the Secretary in conducting the study to "solicit 
and consider the views of State agencies, private firms, institutions 
of higher learning, and other interested persons and governmental 
entities/' 19 

A final report on the findings, conclusions, and recommendations of 
the required study is to be prepared by the Secretary of Commerce and 
submitted to the President and the Congress. The report is to include 
the following : 

(1) A summary of the findings made with respect to each of the 
areas of investigation delineated above ; 

(2) Other findings which are pertinent to the determination 
and implementation of a national policy on weather modification; 

(3) A recommended national policy on weather modification 
and a recommended national weather modification research and 
development program, consistent with, and likely to contribute to, 
achieving the objectives of such policy; 

™ Ibid., spc. 4. itady. 
18 Ibid., sec. 5, report. 


(4) Recommendations for levels of Federal funding sufficient to 
support adequately a national weather modification research and 
development program ; 

(5) Recommendations for any changes in the organization and 
involvement of Federal departments and agencies in weather 
modification which may be needed to implement effectively the 
recommended national policy on weather modification and the 
recommended research and development program ; and 

(6) Recommendations for any regulatory and other legislation 
which may be required to implement such policy and program or 
for any international agreement which may be appropriate con- 
cerning the peaceful uses of weather modification, including 
recommendations concerning the dissemination, refinement, and 
possible implementation of the model domestic code and inter- 
national agreement developed under the specification in the list of 
investigations above. 20 

The act stipulated that the report was to be submitted by the Secre- 
tary within 1 year after the date of enactment of the law ; that is, by 
October 13, 1977. Following a request by the Secretary in June of 
1977 for an extension of this time allotment, a Senate bill was intro- 
duced, providing for an extension of the due date of the report through 
June 13, 1978. No other action on this request was taken, however, 
during the first session of the 95th Congress. Meanwhile, the study 
mandated by Public Law 9J-490 continues under the auspices of the 
Secretary of Commerce. 21 

Congressional direction to the Bureau of Reclamation 

Of special interest as they have affected the weather modification 
activities of the Bureau of Reclamation within the Department of the 
Interior are some laws not specifically concerned with weather modi- 
fication as are the ones discussed above. The Reclamation Act of June 
17, 1902, 22 directs the Bureau to develop water resources for reclama- 
tion purposes, establishing a "reclamation fund,'' which may be used, 
inter alia, "in the examination and survey and for the construction and 
maintenance of irrigation works for the storage, diversion, and devel- 
opment of waters for the reclamation of arid and semiarid lands * * *" 
throughout the 17 contiguous Western States and Hawaii. The author- 
ity of the 1902 act was supplemented by the Fact Finders Act of 
December 5, 1924, and amendments thereto in the act of April 19, 
1945, 23 which enabled the Bureau to conduct "general investigations," 
not related to specific projects, including research work, for the devel- 
opment of water resources without the necessity of making the costs 
thereof reimbursable. 

Thus, the 1902 Reclamation Act, supplemented by the Fact Finders 
Act, provides the authority for the Bureau of Reclamation to engage 
in a program of weather modification research for the purpose of de- 
termining practical methods of inducing precipitation and increased 
runoff that can be stored in surface reservoirs and used for "the rec- 

» Ibid. 

21 This study is underway on behalf of the Secretary of Commerce by a Weather Modifica- 
tion Advisory Board, appointed by the Secretary. See subsequent discussion of activities of 
the Advisorv Board, beginning p. 231. 

M 43 U.S.C. 391 et seq. 

» 43 U.S.C. 377. 


lamation of arid and semiarid lands/' Funds appropriated for weather 
modification research are considered expendable on a nonreimbursable 
basis. 24 

In 1961 the Congress specifically directed the Bureau of Reclamation 
to initiate a program in weather modification through a write-in of 
$100,000 to the fiscal year 190:2 Public Works Appropriation Act. This 
first appropriation for the Bureau's weather modification research 
and development program was added to the Appropriation Act, Public 
Law 87-330 (75 Stat. 722). approved September 30, 19(31. in a con- 
gressional committee of conference, under the heading, "General In- 
vestigations.'' 25 The specific language which directed the weather mod- 
ification research appeared in the Senate report on H.E. 9076, 26 and 
the provision was incorporated into the conference report without 
mentioning weather modification per se. The Senate report included 
the following item : 

Increased rainfall by cloud seeding, $100.000. — The committee recommends al- 
lowance of $100,000 to be used for research on increasing rainfall by cloud seed- 
ing. This amount would be utilized in cooperation with the National Science 
Foundation and the Weather Bureau, which are expected to contribute funds 
and participate in this research. 27 

In accordance with congressional direction in the fiscal year 1962 
Public Works appropriation bill, the Bureau of Reclamation estab- 
lished the Atmospheric Water Resources Management Program 
(^Project Sky water') in 1962. Since the start of this program con- 
gressional direction has continued to be almost entirely through pro- 
visions in the congressional documents relative to annual Public Works 
appropriations. Appendix J is a summary of the appropriation lan- 
guage contained in these documents from 1961 through 1977, which 
provided such direction. It may be noted that by this means the Con- 
gress has continued to provide specific direction to this program al- 
most every year since its inception and has provided frequent funding 
increases, often substantial, over levels budgeted by the administration. 

Legislation providing for temporary authorities to the Secretary of 
the Interior to facilitate emergency actions to mitigate impacts of the 
1976-77 drought was enacted by the Congress and signed by President 
Carter on April 7, 1977. Public Law 95-18 (91 Stat. 36) , subsequently 
amended by Public Law 95-107 (91 Stat. 870) , of August 17, 1977, pro- 
vided authority to appropriate $100 million for a program including 
short-term actions to increase water supplies, to improve water supply 
facilities, and to establish a bank of available water for redistribution. 
The Bureau of Reclamation published rules in the Federal Register 
whereby States could apply for nonreimbursable funds for actions 
designed to augment water supplies. 28 Under these provisions, requests 
for funds to support weather modification activities were received from 
six States. 21 * 

Justus. John R. and Robert E .Morrison, legislative authority for atmosphere research 
by Federal agencips, tbe Library of Congress, Congressional Research Service, Apr. 1, 11*77 
( unpublished), p. 12. 

20 U.S. Congress, committee of eonferenee. public works appropriation bill. 1902; confer- 
ence report to accompany II. R. 9076. Washington. D.C.. U.S. Government Printing Office, 
1961, p. 24. (87th Cong., ist sess. House Rept. No. S7-126S.) 

26 U.S. Congress, Senate, Committee on Appropriations, public works appropriation bill, 
1962 ; report to accompany II. R. 9076. Washington. D.C., U.S. Government Printing Oltice, 
1961. p. i>4. (S7th Cong.. 1st sess. Ho.ise Rept. No. 87-1268.) 

■» Ibid. 

I - eral Register, vol. 42, No. 72. Thursday. Apr. 14. 1977. pp. 19609-19613. 
20 The States were California. Colorado. Kansas. Nevada, North Dakota, and Utah. ?ee 
discussion of the Department of the Interior activities in weather mod iri cat ion. p. 267. for 
amounts of these grants. 




Since 1947 at least 110 bills and 22 resolutions dealing specifically 
with one or more aspects of weather modification have been introduced 
in the Congress. Moreover, many additional pieces of proposed legis- 
lation, providing authorization or appropriations for broader agency 
programs, have given support and/or direction to weather modification 
activities within Federal agencies, often without mentioning such 
activities per se. 

Table 1 summarizes the legislation and resolutions concerned specifi- 
cally with weather modification, which were proposed from the first 
session of the 80th Congress to the first session of the 95th Congress. 
The table shows, for each session, the numbers of bills and resolutions 
pertaining to each of several aspects of the subject and the total number 
of each introduced. The numbers appearing under the several subjects 
of weather modification legislation will, in general, exceed the total 
number of measures introduced in a given year because many of the 
bills were concerned with more than one aspect. It will be noted that a 
total of six laws were passed during this period, as stated earlier. Dur- 
ing the 93d Congress the Senate also passed one resolution, which sup- 
ported the position that the United States should seek the agreement 
of other nations to a treaty banning environmental modification as a 
weapon of war. 


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It can be seen from the table that congressional activity has often 
evolved in accordance with the emergence of various interests and 
issues. Thus, in the 1950's and 1960's there were strong attempts to 
initiate and support Federal research and/or operational programs, 
usually within one or another of several specified departments or agen- 
cies. From time to time emphasis has been given to evaluating weather 
modification technology and establishing a national policy, usually 
: through mandating an in-depth study ; such study was sometimes to be 
undertaken by a select committee established for that purpose. In the 
1970*3 two thrusts in proposed legislation have dealt with regulating 
and or licensing of operations and with reporting weather modifica- 
tion activities to the Federal Government, both reflecting increased 
concern on the part of large segments of the public about unknown 
effects of such operations and about legal and economic ramifications 
of increased or decreased precipitation. Obvious too in the 1970's is the 
reaction of Congress to public concern about the use of weather modi- 
fication as a weapon, as 18 resolutions dealing with that subject were 
introduced in both Houses since 1971. 

Specific measures of recent years on weather modification, those 
introduced in the 94th Congress and the first session of the 95th Con- 
gress, are summarized in the following section. 

Legislation proposed in the 9J/.th and 95th Congress, 1st session 

Proposed legislation and resolutions appearing during the 94th Con- 
gress reflected concern over many current problem areas in weather 
modification coming into focus today, areas over which it is considered 
by many that the Federal Government should have some jurisdiction. 
Based upon a number of specific measures introduced during that Con- 
gress and the ensuing discussions thereon, there emerged the National 
Weather Modification Policy Act of 1976 (Public Law 94-490), which 
could be a landmark, in that studies and decisions pursuant to that act 
may lead to definition of a clear Federal policy for the first time in 
recent years. The bills submitted thus far in the 95th Congress address 
some concerns not dealt with in the recent law and may presage stipula- 
tions which could conceivably be incorporated into future Federal pol- 
icy. Undoubtedly, the 96th Congress will see a greater abundance of 
proposed legislation dealing with Federal policy on weather modifica- 
tion, following receipt by the Congress of the report from the Secre- 
tary of Commerce recommending a national policy and a program of 
Federal research and development. 30 Measures introduced during the 
94th Congress and the first session of the 95th Congress are summarized 
below : 

9ifh Congress, 1st session 

S. 2705. — To provide for a study, within the Department of 
Commerce, by a National Weather Modification Commission, of 
the research needs for weather modification, the status of current 
technologies, the extent of coordination, and the appropriate 
responsibility for operations in the field of weather modification. 
(Hearing was held Feb. 17, 1976.) 

S. 2706. — To authorize and direct the Secretary of Commerce to 
plan and carry out a 10-year experimental research program to 

SP Public Law 94-490 directs the Secretary of Commerce to conduct a study on weather 
modification and to submit a report to the President and the Congress, recommending a na- 
tional policy and a program of Federal research and development in weather modification. 

34-857—79 16 


determine the feasibility of and the most effective methods for 
drought prevention by weather modification. Directs the Secre- 
tary to appoint an Advisory Board and provides for consulta- 
tion with State and local governments starting weather modifica- 
tion efforts for drought alleviation. (Hearing was held Feb. 17, 

S. 2707. — To authorize the Secretary of Commerce to carry out 
a program of assistance to States in preventing and alleviating 
drought emergencies. (Hearing was held Feb. 17, 1976.) 

H.R. 167. — To prohibit the United States from engaging in 
weather modification activities, including cloud seeding and fire 
storms, for military purposes. (No action.) 

H.R. 274-2. — Directed the Secretaries of Agriculture and Inte- 
rior to permit the conduct of weather modification activities, in- 
cluding both atmospheric and surface activities and environ- 
mental research, which are over, or may affect, areas which are 
part of the National Wilderness Preservation System or other 
Federal lands. Authorized the respective Secretaries to prescribe 
such operating and monitoring conditions as each deems neces- 
sary to minimize or avoid long-term and intensive local impact 
on the wilderness character of the areas affected. (No action.) 

H.R. 4325. — Weather Modification and Precipitation Manage- 
ment Act. Authorized the Secretary of the Interior to establish 
precipitation management projects in order to augment U.S. 
usable water resources. Authorized the Secretary to engage in 
operational demonstration projects for potential use in precipita- 
tion management programs in certain States and to settle and 
pay claims against the United States for injury, death, or losses 
resulting from weather modification pursuant to provisions of 
this act. (No action.) 

H.R. 4338. — Designated specific lands within the Sequoia and 
Sierra National Forests, Calif., as the "Monarch Wilderness," 
abolishing the previous classification of the "High Sierra Primi- 
tive Area." Directed the Secretary of Agriculture to authorize use 
of hydrological devices and to provide for weather modification 
activities within such wilderness. (No action.) 

H.R. 10039. — Weather Modification Research, Development, and 
Control Act of 1975. Directed the Secretary of Commerce to es- 
tablish a weather modification research and development pro- 
gram to evaluate the specific needs and uses of weather modifi- 
cation and directed the Secretary to establish a weather modifica- 
tion information system. Prohibited individuals from engaging 
in weather modification activities without obtaining a permit from 
the Secretary and authorized the President to enter into inter- 
national agreements to foster establishment of international sys- 
tems for monitoring and regulation of weather modification ac- 
tivities. (Joint hearings were held on H.R. 10039 and S. 3383, 
June 15-18, 1976 ; no further action on H.R, 10039.) 

77. Res, 28. — Expressed the sense of the House of Rep- 
resentatives that the U.S. Government should seek agreement with 
ot her members of the United Nations on the prohibition of weather 


modification as a weapon of war. (Hearing was held July 29, 1975 ; 
no further action.) 

H. Res. 103.— Same as H. Res. 28. (No action.) 

94th Congress, 2d Session 

S. 3383.— National Weather Modification Policy Act. Directed 
the Secretary of Commerce to conduct a comprehensive study of 
scientific knowledge concerning weather modification and tech- 
nology of weather modification. Required the Secretary to prepare 
and submit to the President and the Congress a final report on 
the findings and conclusions of such study, including a recom- 
mended national policy on weather modification. Extended 
through fiscal year 1980 appropriation authorization for the 
weather modification activities oversight program of the Depart- 
ment of Commerce. (Reported to Senate, May 13, 1976, in lieu 
of S. 2705, S. 2706, and S. 2707; considered and passed by Sen- 
ate, May 21, 1976; hearings held jointly in House subcommittee 
on S. 3383 and H.R. 10039, June 15-18, 1976 ; called up under mo- 
tion to suspend the rules, considered, and passed by the House, 
amended, Sept. 20, 1976; Senate agreed to House amendments, 
Sept. 28, 1976; and approved as Public Law 94-490, Oct. 13, 

H.R. 14S '44- — Extended through fiscal year 1980 appropriations 
authorization for the weather modification activities oversight 
program of the Department of Commerce. ( No action. ) 

95th Congress, 1st Session 

S. 1938.— To extend the National Weather Modification Policy 
Act of 1976 by extending the date for submission of the required 
report of the Secretary of Commerce to June 13, 1978. (No action.) 

H.R. 4069.— Weather Modification Regulation Act of 1977: 
Requires weather modification licenses and permits, establishes 
reporting requirements to be administered by the Secretary of 
Commerce, and requires the Secretary to establish a weather mod- 
ification information system. Authorizes the President to enter 
into international agreements to foster establishment of interna- 
tional systems for monitoring and regulation of weather modifica- 
tion activities. (No action.) 

H.R. 4461— Same as H.R. 2742, introduced during 94th Con- 
gress, first session. (No action.) 

H. Res. 236. — Declares it to be the sense of the House of Repre- 
sentatives that the United States should seek an agreement with 
other members of the United Nations to prohibit research, experi- 
mentation, or the use of weather modification as a weapon. (No 
action.) 31 


Resolutions on toeather modification 

As noted earlier, some 22 resolutions related to weather modification 
have been introduced over the past 30 years in both Houses of the 
Congress. For convenience, data on these resolutions are included along 
witli that on proposed legislation in table 1 and in the discussion 

31 See ch. 10 for a discussion of the development of 6uch a U.N. convention, opened for 
signature in Geneva, May 18. 1977. 


thereon, and three resolutions are included in the preceding list of 
summaries of weather modification bills appearing during the 94th 
and 95th Congresses. 

By far, the largest number of weather modification resolutions, 18 
in all, have been concerned with barring the use of weather modifica- 
tion as a weapon of war. Introduction of such resolutions began during 
the 92d Congress in 1971, and, using similar language, they express 
the sense of either House or of the Congress that the United States 
should seek an agreement with other U.1\ T . members, prohibiting such 
use of environmental modification, including weather modification. In 
1973. the Senate passed S. Res. 71, which had been intro- 
duced by Senator Claiborne Pell. This and other resolutions urging 
prohibition of environmental modification for purposes of warfare 
were prompted by a series of hearings and communications between 
Senator Pell and the Department of Defense on the alleged use of 
weather modification technology as a weapon in Vietnam by U.S. mili- 
tary forces. 32 

Four other weather modification resolutions, introduced in the 1950's 
and 1960 ? s, pertained to the undertaking of comprehensive studies on 
the subject, either by special committees to be established by the Con- 
gress or by departments and/or agencies of the executive branch. 


Cognizant subcommittees of both Houses have conducted hearings 
concerned, at least in part, with Federal weather modification activi- 
ties, from time to time and annually, in connection with oversight of 
agency programs, authorizing legislation, and annual appropriations. 
In addition, more comprehensive hearings on the subject have been 
important parts of the legislative activities leading to passage of the 
major public laws on weather modification, which have been enacted 
since 1953. 

Of particular interest in recent years are the extensive hearings con- 
ducted during 1976 by the Subcommittee on Oceans and Atmosphere 
of the Senate Committee on Commerce 33 and by the Subcommittee on 
the Environment and the Atmosphere of the House Committee on 
Science and Technology. 34 The documents produced from these hear- 
ings contain the testimony of a number of expert witnesses on various 
aspects of weather modification as well as reproductions of numerous 
pertinent documents which were incorporated into the records of the 
hearings. References to documents on other weather modification hear- 
ings conducted in recent years are contained in the bibliography of 
congressional publications in appendix H. 

On October 26, 1977, the Subcommittee on the Environment and the 
Atmosphere of the House Committee on Science and Technology con- 
ducted a special hearing on the National Weather Modification Policy 
Act of 1976 (Public Law 94^90) . Among other witnesses, Mr. Harlan 
Cleveland. Chairman of the Commerce Department's Weather Modi- 

-' The correspondence and hearings on the use of weather modification as a weapon in 
Vietnam and of the development of a U.N. treaty barring environmental modification in war- 
far* are discussed among other international aspects of weather modification in ch. 10. 

"' ; U.S. Congress, Senate. Committee on Commerce. Subcommittee on Oceans and Atmos- 
phere. Atmospheric Research Control Act. hearing. 94th Cong., 2d sess., on S. 2705. S. 2706, 
and S 2707. Feb. 17. 1976, Washington, U.S. Government Printing Office, 1976. 297 pp. 

M TVS. Congress. House, Committee on Science and Technology, Subcommittee on the En- 
vironment and the Atmosphere. Weather modification, hearings, 94th Cong.. 2d sess.. on 
TT i: ino?,f> and S. 3383, June 15-18, 1976, Washington, U.S. Government Printing Office, 
1976, 524 pp. 


fication Advisory Board, briefed the subcommittee on progress of the 
Board in carrying out for the Secretary of Commerce the comprehen- 
sive study required by the act and also reported on findings of the 
Board to date in a discussion paper which he submitted for the record. 33 

Studies and reports by congressional support agencies 

In addition to the studies and reports of the executive branch which 
were mandated by the Congress through legislation, studies have also 
been undertaken on behalf of the Congress by congressional support 
agencies on at least three occasions. The present report, requested in 
1976 by the Senate Committee on Commerce, was preceded by a similar 
study and report requested a decade earlier by the same committee. 36 
In 1974, the General Accounting Office (GAO) conducted a critical 
review of ongoing Federal research programs in weather modification 
and prepared a report to the Congress on the need for a national pro- 
gram. 37 A discussion of the findings and recommendations of this GAO 
study, along with those of other major Government and non-Govern- 
ment studies, is undertaken in a later chapter of this report. 3S 

Activities of the Executive Branch 

The executive branch of the Federal Government sponsors nearly 
all of the weather modification research projects in the United States, 
under a variety of programs scattered through at least six departments 
and agencies. The National Atmospheric Sciences Program for 19 7S 39 
includes information on specific programs of the Departments of Agri- 
culture, Commerce, Defense, and the Interior and of the Energy Re- 
search and Development Administration (now part of the Department 
of Energy) and the National Science Foundation. In recent years 
weather modification research programs were also identified by the De- 
partment of Transportation and the National Aeronautics and Space 

In addition to specific programs sponsored by Federal agencies, there 
are other functions relevant to weather modification which are per- 
formed in several places in the structure of the executive branch. Vari- 
ous Federal advisory panels and committees and their staffs, which 
have been established to conduct in-dep>th studies and prepare compre- 
hensive reports, to provide advice and recommendations, or to coordi- 

35 Cleveland. Harlan, "A U.S. Policy To Enhance the Atmospheric Environment." A dis- 
cussion paper by the Weather Modification Advisory Board, Oct. 21, 1977. Submitted as part 
of testimonv in hearing: U.S. Congress. House of Representatives, Committee on Science 
and Technology. Subcommittee on the Environment and the Atmosphere, "Weather Modi- 
fication." 95th Cong., 1st sess., Oct. 26, 1977, Washington, D.C., U.S. Government Printing 
Office, 1977, pp. 2-49. 

36 U.S. Library of Congress, Legislative Reference Service, "Weather Modification and Con- 
trol," a report prepared by Lawton M. Hartman and others for the use of the Committee on 
Commerce. U.S. Senate, Washington, D.C., U.S. Government Printing Office, Apr. 27, 1966, 
181 pp. (89th Cong., 2d sess., Senate Rept. No. 1139.) 

87 Comptroller General of the United States, "Need for a National Weather Modification 
Research Program," report to the Congress, U.S. General Accounting Office, Washington, 
B.C., Aug. 23, 1974, 71 pp. 

38 See eh. 6. p. 324. 

39 The National Atmospheric Sciences Program, including the Federal program in weather 
modification, is published annually in a report of the Interdepartmental Committee for 
Atmospheric Sciences. The most recent such report, containing a discussion of and funding 
for the fiscal year 1978 program is the following : Federal Coordinating Council for Science, 
Engineering, and Technology. Committee on Atmosphere and Oceans, Interdepartmental 
Committee for Atmospheric Sciences. National Atmospheric Sciences Program, fiscal year 
1978, ICAS 21-FY78, September 1977, pp. 87-94. 


hale Federal weather modification programs have been housed and 
supported within executive departments, agencies, or offices. For exam- 
ple, the National Advk^iy Committee on Oceans and Atmosphere 
(XACOA) and the Weather Modification Advisory Board are sup- 
ported through the Department of Commerce. While the membership 
of the Interdepartmental Committee for Atmospheric Sciences 
(ICAS) comes from each of the Federal departments and agencies 
with atmospheric science programs, its staff has been housed in the 
National Science Foundation. 

The program whereby Federal and non-Federal U.S. weather mod- 
ification activities are reported to the Federal Government is adminis- 
tered by the National Oceanic and Atmospheric Administration 
(XOAA) within the Department of Commerce. Under this program a 
central file is maintained on all such projects in the United States, 
and summary reports on these projects are published on a nearly 
annual basis by NOAA. 

The United States has been active in at least two areas of interna- 
tional interest in weather modification. One aspect has been the efforts 
through the United Nations to promote the adoption of a treaty bar- 
ring weather modification as a military weapon. There is also a U.S. 
interest in international efforts to modify the environment for bene- 
ficial purposes. The State Department is active in negotiating agree- 
ments with other countries which might be affected by U.S. experiments 
and has also arranged for Federal agencies and other U.S. investiga- 
tors for participation in international meterological projects, includ- 
ing weather modification, under the World Meteorological Organiza- 
tion (WMO). These activities are discussed in more detail in a subse- 
quent chapter on international aspects of weather modification. 40 

In the next subsection there is an attempt to describe the Federal 
organizational structure for weather modification, at least to the extent 
that such a structure exists, has existed, or may exist in the near 
future. Other subsections address Federal coordination and advisory 
groups, the weather modification activities reporting program, and 
the array of Federal studies and reports which have been undertaken 
by the executive branch, either as required by law or initiated within 
the branch. A summary of the Federal research program and detailed 
descriptions of each of the several agencies programs in weather modi- 
fication are contained in a separate major section at the end of this 
chapter. 41 



Cum nt status of Federal organization for weather modification 

The present Federal structure of weather modification research 
activities is characterized esseiitially by the mission-oriented approach, 
where each of six or seven deportments and agencies conducts its 
own program in accordance with broad agency goals or under specific 
directions from the Congress or the Executive. The exception to this 
approach is the program of the Xational Science Foundation, whose 
funded weather modification research activities have included a broad 

<° Spp en i o. 
11 See p. 241 ff. 


range of individual fundamental problem investigations, research 
supporting some aspects of the project of other Federal agencies, 
and conduct of major projects initiated by the Foundation. The pro- 
grams of the several agencies have been loosely coordinated with others 
through various independent arrangements and/or advisory panels 
and particularlv through the Interdepartmental Committee for At- 
mospheric Sciences (ICAS). The ICAS, established in 1959 by the 
former Federal Council for Science and Technology, provides advice 
on matters related to atmospheric science in general and has also been 
the principal coordinating mechanism for Federal research in the 
field of weather modification. The following observation on the cur- 
rent Federal weather modification organizational structure was stated 
recently by the chairman of the ICAS : 

Organization [s] doing the research [should] be knowledgeable of the sector 
of the public that is to be involved with special weather modification techniques. 
There is no single agency within the Government that knows all of the problems 
of society vis-a-vis weather modification. As things stand, the individual weather 
modification programs being carried out by the various ICAS member agencies 
are being pursued in concert with the missions of those agencies. 42 

The nature of the present Federal organizational structure for 
weather modification is related to and results from the prevailing 
policy, or lack of such policy, currently subscribed to by the Federal 
Government regarding weather modification. The clearest statement 
of such a policy came in a reply to a 1975 letter from Congressmen 
Gilbert Gude and Donald M. Fraser and Senator Claiborne Pell, 
addressed to the President, urging that a coordinated Federal program 
in the peaceful uses of weather be initiated. 43 In the official response 
from the executive branch, written by Norman E. Ross, Jr., Assistant 
Director of the Domestic Council, the current Federal weather modifi- 
cation policy was affirmed : 

We believe that the agency which is charged with the responsibility for deal- 
ing with a particular national problem should be given the latitude to seek 
the best approach or solution to the problem. In some instances this may involve 
a form of weather modification, while in other instances other approaches may 
be more appropriate. 

While we would certainly agree that some level of coordination of weather 
modification research efforts is logical, we do not believe that a program under 
the direction of any one single agency's leadership is either necessary or 
desirable. We have found from our study that the types of scientific research 
conducted by agencies are substantially different in approach, techniques, and 
type of equipment employed, depending on the particular weather phenomena 
being addressed. * * * Each type of weather modification requires a different form 
of program management and there are few common threads which run along 
all programs. 44 

Recently, the Chairman of the Commerce Department's Weather 
Modification Advisory Board, Harlan Cleveland, expressed the 
Board's opinion of the current Federal policy and structure : 

The United States does not now have a weather modification policy. The 
three main Federal actors in weather modification research are NOAA in the 

42 Testimony of Dr. Edward P. Todd In U.S. Congress, House of Representatives, Commit- 
tee on Science and Teehnolosy, Subcommittee on the Environment and the Atmosphere, 
'Weather Modification." hearings. 94th Cong., 2d sess.. June 15-18, 1976. Washington. D.C., 
T.S. Government Printing Office, 1976, p. 81. 

43 Gude. Gilbert. "Weather Modification." Congressional Record. June 17. 1975, pp. 19201- 
192f>3. (The statement in the Congressional Record, including the letter to the President 
and the official reply, are reproduced in app. A.) 

" Ibid. 


Department of Commerce, the Bureau of Reclamation in the Department of 
the Interior, and the National Science Foundation. . . . Their combined R and D 
efforts can only be described as fragmented and famished, living from hand to 
mouth on each agency's relationship with a different congressional subcommittee, 
with no sense of a national policy or program. . . . The agencies that are involved, 
and their university and other contractors and grantees, have developed, despite 
the fragmentation, remarkably effective informal relationships which make 
the coordination and mutual assistance better than the division of roles and 
missions would indicate. 45 

A somewhat different viewpoint, but related in several points to the 
preceding opinions w*as expressed in 1976 by Dr. Ronald L. Lavoie, 
Director of NOAA's Environmental Modification Office, addressing 
the second meeting of the North American Interstate Weather Modifi- 
cation Council : 

Let me address the question of current Federal policies in weather modifi- 
cation — the statement has been made that there aren't any. I think that I must 
disagree with that statement. There are, in fact, such policies although they 
are perhaps unobtrusive or low-key. They certainly aren't propounded very 
loudly, but I think it is safe to say that there is some Federal policy on weather 
modification. . . . For example, in the area of research and operations the Federal 
policy, or you may call it strategy, is to leave it to the specialized agencies to 
fund research and to develop or apply weather modification in carrying out their 
particular missions. One can argue with this policy ; nevertheless, it does 
exist. . . . One shouldn't get the impression, however, that this is an entirely 
fragmented effort. . . . There is some coordination or integration, at least in the 
sense that technocrats responsible for advising the agencies in these matters get 
together to discuss issues and share problems Nevertheless, there is no Fed- 
eral or national commitment to weather modification, and I believe that this is 
what was implied when it was said that there was no national policy.* 8 

Yet another observation on the subject of Federal organization is 
that expressed in the 1974 report by the U.S. General Accounting 

Our review of the Federal weather modification research activities supports 
the findings of nearly a decade of studies. These studies conducted by scientific 
panels, committees, and other groups all identified common problems — ineffec- 
tive coordination, fragmented research, and research efforts that are subcritical 
(funded below the level necessary to produce timely, effective results). Most 
studies proposed a common solution. What was needed, in essence, was a 
national research program under a single Federal agency responsible for estab- 
lishing plans and priorities, obtaining the needed funds from the Congress, 
managing research efforts, and accounting for the results its programs achieved. 

To date, except for the establishment of several coordinating committees, 
subcommittees, and advisory panels — none of which have the authority to take 
action to correct problems already identified — an effective overall national 
weather modification research program has not been established. 47 

There is some consensus that the apparent fragmentation and lack 
of a cohesive Federal effort have not only prevented the growth of a 
strong, adequately funded research program but may have also 
retarded progress in development of weather modification technology 

45 Cleveland, Harlan. "A U.S. Policy To Enhance the Atmospheric Environment." A dis- 
cussion paper by the Weather Modification Advisory Board, Oct. 21, 1977. (Submitted as 
part of testimony in hearing : U.S. Congress, House of Representatives, Committee on Sci- 
ence and Technology. Subcommittee on the Environment and the Atmosphere, "Weathel 
Modification," Oct. 26, 1977. p. 41.) 

49 Lavoie, Ronald L.. "Effects of Legislation on Federal Programs and the Prospect of Fed- 
eral Involvement." In proceedings of Conference on Weather Modification, Today and Tomor- 
row : second annual meeting of the North American Interstate Weather Modification Coun- 
cil, Kansas City, Mo., Jan. 15-16. 1976, pub. No. 76-1, pp. 56-57. 

*" Comptroller General of the United States. "Need for a National Weather Modification 
Research Program." report to the Congress. U.S. General Accounting Oftlce, B-133202, Wash- 
ington, D.C., Aug. 23, 1974, p. 3. 


itself. Many feel strongly that assignment of a "lead agency" would 
solidify and strengthen the Federal effort. To others, however, "* * * 
the present structure for Federal Government activity in weather mod- 
ification appears to be working satisfactorily," 48 and the existence of 
separate agency programs fosters increased understanding through 
independent research projects and through the cross- fertilization of 
ideas and exchange of findings achieved in cooperative projects, in 
professional meetings, and through program-level coordination. 

In a recent Federal study on weather modification, a subcommittee 
of the Domestic Council could not reach a consensus on the proper 
institutional structure for planning and management of the national 
weather modification research effort. Consequently, both of the posi- 
tions noted above were identified as options for such Federal 
structure : 49 

Option (1) : Continue coordination and planning of the national 
weather modification effort through the Interdepartmental Committee 
for Atmospheric Sciences of the Federal Council for Science and 
Technology, with individual agencies pursuing their mission responsi- 

Option (2) : Establish a lead agency to foster the broad advance- 
ment of the science and technology of weather modification as 
recommended by the National Advisory Committee on Oceans and 
Atmosphere, the National Academy of Sciences, and other groups to 
coordinate and plan the national effort with the assistance and partici- 
pation of other agencies. 

Those who espouse the latter position feel that the lead agency 
responsibility should include the following functions : 50 

The lead agency would assume the leadership for planning the 
Federal weather modification program, in concert with those other 
concerned agencies, universities, and the private sector. 

The lead agency would present, within the executive branch, a 
consolidated national weather modification research plan and be 
available to represent the national plan before the Congress. 

The lead agency would, within the framework of the joint plan- 
ning effort, encourage and assist in justifying programmatic ac- 
tivities in other agencies that might contribute significantly to the 
national weather modification objectives, especially when those 
programs can be implemented as supplements to the agencies' 
ongoing mission-related activities. 

The lead agency would take on the responsibility for presenting 
the budgetary requirements to carry out the national plan to the 
Office of Management and Budget and, with due consideration of 
overall priorities of the agency, would seek to provide within its 
own budget for activities essential to the national plan and not 
incorporated in the budgets of the other agencies. 
The history of the organization of the Federal program in weather 
modification, to the extent that such a structure has existed, can be 

4 * Testimony of Dr. Alfred J. Esgers. Jr.. Assistant Director for Research Applications, 
National Science Foundation in U.S. Congress. House of Representatives. Committee on 
Seienr-e and Technology. Subcommittee on the Environment and the Atmosphere. "Weather 
Modification. " v>earin£s. 04th Consr.. 2d sess., June 15-1S, 1976, Washington, D.C., U.S. Gov- 
ernment Printing: Office. 1976. p. 109. 

49 U.S. Domestic Council. Environmental Resources Committee. Subcommittee on Climate 
Change, "The Federal Role in Weather Modification." Washington, D.C, December 1975, 
p. 19. 

60 Ibid., app. A, pp. A-2 and A-3. 


conveniently divided into three periods, each roughly a decade long. 
These periods and the characteristics of the Federal organization dur- 
ing each are discussed briefly below. 

Federal structure; 194-6-57 

As seen in the earlier historical account of weather modification, in 
the period from 1946 through 1957 practically all projects in the 
United States were conducted by private individuals and by industry 
supported through private funds. What activities the U.S. agencies 
did support were both mission oriented and mostly uncoordinated. The 
Defense Department developed an early research program, specifically 
in seeding technology and hardware. Since World War II, the Air 
Force had a continuing need to dissipate fog, and the Korean war and 
SAC missions during this period required airports to be open to permit 
unrestricted flights. The Navy developed a strong research capability 
at its China Lake, Calif., laboratory, concentrating on seeding de- 
vices and materials. Project Cirrus, a joint project of the Army Signal 
Corps, the Navy, and the Air Force, was initiated by the Defense 
Department in 1947 and continued through 1952. 

Civilian implications for weather modification were investigated 
by the U.S. Weather Bureau of the Commerce Department in 1948 as 
part of its cloud physics program. The Bureau's early position, how- 
ever, seemed to lack enthusiasm for a research program at the time, 
largely reflecting agency conservatism and some unwillingness to be 
caught up in a technology that was fraught with exaggerated claims 
of commercial rainmakers. 51 This early negative outlook of the 
Weather Bureau was modified in the late 1960's when its successive 
parent organizations, the Environmental Science Services Adminis- 
tration (ESSA) and the National Oceanic and Atmospheric Admin- 
istration (NOAA), inaugurated a fresh interest in a weather modifi- 
cation research program. The Weather Bureau did participate with 
the Navy in project SCUD in 1953-54 along the east coast, in an 
attempt to modify the behavior of extratropical cyclones by artificial 

The third Federal agency conducting weather modification re- 
search during this period was the Forest Service of the U.S. Depart- 
ment of Agriculture, which in 1953 initiated Project Skyfire, aimed 
at suppressing lightning, a major cause of forest fires. This project 
received joint support later during the 1960's from the National Sci- 
ence Foundation, and. until its demise in 1976. was the longest run- 
ning single Federal weather modification research project. 

Confusion and uncertainty in the state of weather modification, 
owing to a mixed reaction to achipA-oments and claims of achieve- 
ment of weathor modification operators and to the lack of a cohesive 
research program in the Federal Government, led to the establish- 
ment in 1953 of the Advisory Committee on Weather Control, by 
Public Law 83-256. During the conduct of the intensive investiga- 
tion of the subject by the Advisory Committee between 1953 and 

r>1 Communications from F. W. Reichelderfer. Chief of the U.S. Weather Bureau, in U.S. 
Congress. Senate. Committees on Interior and Insular Affairs. Interstate and Foreign Com- 
merce, and Agriculture and Forestry, "Weather Control and Augmented Potable Water 
Supply," Joinl hearings, ,92d Cong., 1st sess.. Mar. 14. 15, 16, 19 and Apr. 5, 1951, Washing- 
ton, D.C., U.S. Government Printing Office, 1951, pp. 37^17. 


1957. the committee seems to have provided somewhat of a coordina- 
tion function and even some modicum of direction to the Federal 
effort it was studying. There was support in the Congress for both 
the formulation and the Federal management by the Advisory Com- 
mittee of a 5-year Federal-State weather modification research pro- 
gram, to be conducted by the committee, the States, universities, and 
private institutions. 52 The Advisory Committee favored an existing 
Federal agency, however, for this proposed management function. 

Federal structure; 1958-68 

The Advisory Committee, reporting in 1957, provided a setting 
for progress over the next 10 years, as it presented elements of a 
national policy and guidelines for future development of a research 
program. A former NSF program manager for weather modifica- 
tion, Earl G. Droessler, recently praised the work of the Advisory 
Committee : 

The Committee did a remarkable job for weather modification. Perhaps, most 
importantly, its careful study and reporting in the 1950's gave a measure of 
respect, cohesion, and momentum for the field of weather modification, and 
thus provided a setting for progress over the next decade and more. Prior to 
the work of the committee, the field was plagued with tension and 
uncertainty. 53 

Encouraging a wide research program in meterology as the essen- 
tial foundation for understanding weather modification, the Ad- 
visory Committee named the National Science Foundation as its rec- 
ommended agency for sponsoring the required research program. 
Accordingly, the Congress, when it enacted Public Law 85-510, di- 
rected the NSF to initiate and support a program in weather modi- 
fication and effectively named the NSF as lead Federal agency for 
weather modification. 

Weather modification research enjoyed a position of high value 
and priority among the top leadership of the Foundation. 54 The XSF 
promoted a vigorous research program through grants to universi- 
ties, scientific societies and the National Academy of Sciences, in- 
dustry, and agencies of the Federal Government and established 
an Advisory Panel for Weather Modification, which reported to 
the Foundation. A series of 10 annual reports on weather modifica- 
tion were published by the NSF for fiscal years 1959 through 1968. 
Recognizing the severe shortage of trained personnel, the NSF es- 
tablished the policy of financing graduate and postgraduate train- 
ing as part of its grant support program, stating in its second annual 
report, "In the field of weather modification our greatest deficiency 
today is skilled manpower." 55 

At the working level, representatives of nine Government agencies 
were called together by the NSF to form the Interagency Conference 
on Weather Modification to afford a mechanism for communication on 
weather modification activities and to plan and develop cooperative 

32 See. for example. S. 86 and companion House bills. H.R. 3631. H.R. '5232, H.R. 5954, 
and H.R. 5958. introduced in the 85th Congress during 1957. 

53 Droessler. Earl G.. "Weather Modification : Federal Policies. Funding from all Sources, 
Interagency Coordination," background paper prepared for the U.S. Department of Com- 
merce Weather Modification Advisorv Board. Raleigh, N.C., Mar. 1, 1977, p. 1. 

"Ibid., p. 2. 

5r> National Science Foundation. "Weather Modification ; Second Annual Report for Fiscal 
Year ended June 30, 1960." Washington. D.C.. U.S. Government Printing Office, June 16, 
1961. p. 1. 


projects. 56 Joint Federal projects were established between the Foun- 
dation- and the Departments of Agriculture, Commerce, and Interior. 
During this period the Congress, wanting to support more applied re- 
search directed toward a major problem, such as requirements for more 
precipitation in the West, appropriated funds for what was to become 
a major weather modification program under the Bureau of Reclama- 
tion in the Department of the Interior. The Foundation warmly en- 
dorsed the Bureau of Reclamation's "Project Sky water" and has since 
funded many of the research projects associated with this program. 57 

Fi deral structure; 1968-77 

The lead agency responsibilities and authorities of the National 
Science Foundation acquired in 1958 under Public Law 85-510 were 
abrogated by Public Law 90-407, enacted July 18, 1968, which became 
effective September 1, 1968. A lapse in Federal policy and Federal 
structure has since occurred as a result of congressional and executive 
inaction, although after a hiatus of over 3 years, some responsibility 
was given to XOAA in 1971; namely, that for collecting and dis- 
seminating information on weather modification projects in the United 
States. This requirement, directed by Public Law 92-205, of Decem- 
ber 18, 1971, has been the single Federal weather modification function 
prescribed by law until 1976, when Public Law 94-490 required the 
Secretary of Commerce to conduct a study to recommend a national 
policy and a research program in weather modification. The lead 
agency responsibility has never been reassigned, and Federal leader- 
ship for research purposes is dispersed among the several agencies. 

The only semblance of weather modification leadership in the Fed- 
eral structure during this period has been through the coordination 
mechanism of the Interdepartmental Committee for Atmospheric Sci- 
ences (ICAS). The ICAS has established some policy guidelines and 
has sponsored activities, such as the annual interagency weather modi- 
fication conferences, intended to foster cooperation among agency 
programs. It has not assumed a management role nor has it sought to 
intervene in the budgeting processes by which the several agency pro- 
grams are supported. The activities of the ICAS are discussed in more 
detail in a section to follow on coordination of Federal weather modi- 
fication activities. 

Future Federal organization for weather modification 

The present intensive study underway within the Department of 
Commerce, as directed by the National Weather Modification Policy 
Act of 1976, Public Law 94-490, mav be laying the groundwork for a 
clear Federal policy in weather modification, after a 10-year lapse in 
Federal leadership and two decades after the first major Federal 
wpp.ther modification study wns submitted to the President and the 
Concrress. The new approach will benefit from scientific and technical 
advnn^os as well as the greater attention which has been given in recent 

54 t< n annual interaerpnev conferences on weather modification wore sponsored by the 
National Seience Foundation throujrh 10f»S. Since that year, when the lead asrency role was 
f n1 - Pn from t | lfl -yQ-p r, v public Law 00 407. the annual interagency conference has been 
sponsored by the Interdepartmental Committee for Atmospheric Sciences (TCAS>. The 11th 
conference sponsored by ICAS. was conducted by the NSF at t^e request of ICAS : banning 
with tbe 12th. the annual conference have been conducted by NO A A. at the request of ICAS, 

th %°Pr C ^ess1 — "^Weather Modification: Federal Policies, Funding from all Sources, Inter- 
agency Coordination," 1977, p. 4. 


years to legal, social, economic, ecological, and international aspects 
of the subject. Part of the national policy which will presumably be 
established by the Congress following the study (very likely during 
the 96th Congress) will be a reorganized or reconstituted Federal 
structure for leading and managing the Federal activities in weather 

Kecognizing that most studies of the past decade have proposed solv- 
ing the apparent fragmentation of Federal projects and responsibil- 
ities by redesignating a lead agency, and also observing some of the 
objections and shortcomings of such a designation, the Commerce De- 
partment's Weather Modification Advisory Board has considered vari- 
ous options for structuring the Federal program. One possible option 
the Board is considering in its study is the creation of a special agency 
for weather modification, "with a mandate to learn what needs to be 
learned about weather modification and to insure regulation of its 
practice," 58 The new agency would "plan, budget, spur, supervise, and 
continually evalute a Federal program of research and development, 
designed to enhance the atmospheric environment." Under this concept 
existing agency projects would become part of a coordinated Federal 
effort, and future projects would be presented to the Congress and to 
the Executive "as an understandable part of a coherent R and D 
strategy." 59 

The Advisory Board has had difficulty in deciding where such a new 
agency should be placed in the executive structure. Presumably it could 
be made part of an existing structure or it could be established as a 
"semi-autonomous" agency attached to an existing department for ad- 
ministrative purposes and support. With the creation of a Department 
of Natural Resources, as has been proposed, a logical departmental 
home for the suggested weather modification agency would be found. 
The Board further suggests that such a new agency, regardless of its 
location in the Federal structure, should work closely with a small 
(five- to nine-member) Advisory Board, composed of people ac- 
quainted with atmospheric sciences, user needs, operational realities, 
advantages of costs and benefits, and "the broader national and inter- 
national issues involved." 60 

The current thinking of the Weather Modification Advisory Board 
also includes a laboratory center as part of the proposed new agency, 
one newly established or an existing Federal laboratory converted to 
weather modification research. While some research and development 
would be conducted "in house" by the agency, portions of the coordi- 
nated research effort would be allocated to other Federal agencies or by 
contract to universities and other non-Federal institutions. 61 

Droessler has also observed increased individual support for the con- 
cept of a weather modification national laboratory. lie suggests that 
the location of such a center in the Federal structure should be deter- 
mined by its principal research thrust. If basic scientific research, such 
as that which "undergirds" weather modification applications, is pri- 
mary, he suggests that NSF should have the responsibility. If the focus 
of the new proposed laboratory should be on severe storm amelioration, 

58 Cleveland, "A U.S. Policy to Enhance the Atmospheric Environment," discussion paper 
by thp Weather Modification Advisorv Board. Oct. 21, 1977, pp. 23-24. 
69 Ibid., p. 24. 

60 Ibid. 

61 Ibid., p. 25. 


including hurricane research, NO AA should be the management choice. 
Finally, if research of the new laboratory is aimed toward the impacts 
of weather modification on agriculture, the U.S. Department of Agri- 
culture should be directed to establish and manage the facility. 62 

A number of bills were introduced in the Congress from time to time 
which would have established within one agency or another a single 
agency with responsibility for managing a Federal weather modifica- 
tion program. For example, S. 2875 in the 89th Congress would have 
created in the Department of the Interior a central scientific and en- 
gineering facility and regional research and operations centers. In the 
same Congress, S. 2916, which did pass the Senate, would have pro- 
vided much the same structure within the Department of Commerce. 
Both bills permitted weather modification research in support of mis- 
sions by the other Federal agencies, but established a focal point for 
research and for other management functions in the Department of the 
Interior or the Department of Commerce, respectively. 63 

In addition to management of Federal research programs and co- 
ordination of these programs, the Federal weather modification orga- 
nizational structure must also be concerned with other functions. These 
could include planning, project review, data collection and monitoring, 
regulation, licensing, and indemnification. The institutional arrange- 
ment within which these activities are handled could be part of the 
agency with prime research responsibility, or some or all of these func- 
tions could be assigned elsewhere. For example, the State Department 
will presumably continue to exercise appropriate authorities with 
regard to international programs or U.S. programs with potential 
impacts on other nations, though responsibility for cooperation on 
the scientific and technical aspects of such projects would quite natur- 
ally be given to one or more research agencies. Assignment of some of 
these functions might be to other agencies or to special commissions, 
established as in some States, to deal with regulation, licensing, and 

Grant argues that "the extensive multidisciplinary nature of and 
the potential impact on large segments of society by weather modifica- 
tion demands great breadth in the organizational structure to manage 
the development of weather modification." 64 He continues : 

In view of these complex involvements and interactions, it is clear that the 
governmental organizational structure needs to he much broader than the mis- 
sion interests of the respective Federal agencies. Presently, coordination is 
effected through ICAS. More is required. The present program in weather modi- 
fication is too fragmented for optimal utilization of resources to concentrate on 
all aspects of the priority problems. Weather modification has not moved to the 
stage where research should be concentrated in the respective mission agencies. 

Many of the priorities and problems are basic to weather modification itself 
and must l>e resolved and tested before emphasis is placed on the respective mis- 

62 Droessler, "Weather Modification : Federal Policies, Funding From All Sources, Inter- 
agency Coordination." 1!)77. pp. 10—11. 

•> For analysis of these and other related bills concerned with Federal organization for 
weather modification see Johnson. Ralph W.. "Federal Organization for Control of Weather 
Modification." In Howard J. Taubenfeld (editor), "Controlling the Weather," New York. 
Dunellen. 1970. pp. 145-158. 

64 Grant. Lewis (>.. testimony in : U.S. Congress, House of Representatives, Committee on 
Science and Technology, Subcommittee on the Environment and the Atmosphere. "Weather 
Modification." hearings, 04th Cong.. 2d sees., June 15-18, 1977. Washington, D.C.. U.S. 
Government Frinting Office, 1976, p. 290. 


sion users. Present fragmentation of effort, combined with subcritical support 
levels, retards adequate progress toward the goal of problem resolution and de- 
velopment of application capability. 

I suggest that a commission-type approach be considered. This would permit 
representation of various weather modification missions by researchers, users, 
and the general public. Such a commission could develop a comprehensive and 
coordinated national weather modification policy and program of weather modi- 
fication research. ... A positive national program and funding levels could be 
recommended to Congress. I believe that management of the program through 
this commission for the next five to ten years should also be considered. The 
highest standards possible and the broadest representation possible should be 
required for this commission and its staff. 

As the technological capability develops and can respond to various uses, the 
lull responsibility for the respective uses could transfer to the mission agencies 
at that time. Continued involvement by the agencies during the development 
stages could make a smooth transition possible. If the national research and 
development program is organized and managed through such a commission, the 
commission should not have the dual role of regulating weather modification at 
the same time it has the responsibility for its developmient. 85 

Changnon has recommended an almost total reorganization of the 
Federal weather modification structure in order to handle better the 
current major research responsibilities; evaluation efforts needed im- 
mediately, which are not being addressed ; and readiness to perform re- 
sponsibilities of the near future, including operations, regulation, and 
compensation. He suggests tw r o approaches to this reorganization, 
shown schematically in figure l. 66 

In his first approach, Changnon would place all weather modifica- 
tion activities, except regulation and compensation, in one agency 
(Agency X, fig. la), either a new agency or a division of one exist- 
ing. From a weather modification and a user standpoint the likely can- 
didates proposed among existing agencies are the U.S. Department of 
Agriculture and XOAA. This primary agency would develop a na- 
tional laboratory which would both conduct research and development 
and also subcontract such efforts. The agency and its laboratory would 
be responsible for program design, monitoring, and evaluation of all 
experimental and operational projects and would report results to the 
regulatory agency (Agency Y, fig. la). The laboratory would also 
be responsible for Federal operational efforts and for development of 
guidelines for private operators. Close interaction would be required 
with the States, private business, and the public within operational 
regions. Agency Y could be a new agency or an existing one, such as 
the Environmental Protection Agency or XOAA. provided that NOAA 
is not also chosen as Agency X. Agency Y would also develop and ad- 
minister compensatory mechanisms to benefit those identified as losers 
as a result of weather modification programs. This first approach would 
also include a Presidential board or commission of appointed non- 
Federal members with statutory responsibility for reporting annually 
to the President and the Congress on all weather modification activi- 
ties performed by Agencies X and Y. 67 

05 Ibid., pp. 290-291. 

66 Changnon. Stanley A.. Jr.. "The Federal Role in Weather Modification." background 
paper prepared for the U.S. Department of Commerce Weather Modification Advisory 
Board. Urbana. 111., Mar. 9. 1977, pp. 24-27. 

87 Ibid., pp. 25-26. 



In Changnon's second organizational approach, there are similarities 
to the first, but current research activities would be retained with some 
Federal agencies (see fig. lb). Agency Y would handle regulatory- 
compensatory functions as in the first approach, and a Presidential 
board or commission would make critical annual assessments of the 
progress and activities in all agencies as well as report annually to the 
President and the Congress. A major agency, new or existing, would 
have direct responsibility for its own activities as well as the research 
programs of other Federal agencies. Thus, existing programs of the 
Departments of Agriculture, Commerce, and Defense and of the Na- 
tional Science Foundation would continue, but under direction of 
Agency X, each program directed toward specific agency missions. 
Other agencies currently involved in weather modification — the De- 
partments of Energy, Interior, and Transportation, and the National 
Aeronautics and Space Administration — would be stripped of their 
programs. 68 

In his 1970 paper, Johnson explored some of the more plausible in- 
stitutional arrangements that could be designed for Federal manage- 
ment of weather modification. 69 He identified the various functions 
into which such management responsibilities could be divided and at- 
tempted to show the optimum ways that each function might be 
handled. A major point which Jolmson made then, which is still ap- 
propriate today, is that the Federal institutional arrangements should 
depend on the pace of the development of weather modification tech- 
nology. Thus, establishment of a full-blown structure dealing with all 
weather modification functions may not yet be advisable, even in 1973. 



There are a number of formal and informal mechanisms by which 
the Federal research program in weather modification is coordinated, 
and there exist a variety of panels, committees, and organizations — 
some governmental and some quasi-governmental — which provide ad- 
vice and a forum for exchange of information on various aspects of 
weather modification. Coordination is also achieved through profes- 
sional society meetings and through workshops on specific problems 
which are scheduled by Federal agencies from time to time. 

Much of the coordination of weather modification projects attempted 
by agency representatives consists of exchange of information on the 
scope and the funding of the different agency programs, this ex- 
change accomplished through meetings of committees, conferences, 
and panels. Through such exchange it is expected that consensus can 
be approached and coordination achieved. 

Various opinions have been expressed on the degree to which Fed- 
eral weather modification programs are coordinated. According to 
Droessler, "The weather modification research program probably is 
as well coordinated as any research effort within the Federal Govern- 

68 Ibid., p. 26-27. 

89 Johnson, "Federal Organization or Control of Weather Modification," 1970, pp. 131-1S0. 

34-SoT— 79 17 


ment." 70 Dr. Alfred J. Eggers, Jr., former Assistant Director for Re- 
search Applications at the S"SF has recently stated that : 

In summary, the current programs in weather modification of the various 
agencies appear to be sufficiently well coordinated to avoid unknowing duplica- 
tions of efforts, but not so rigidly coordinated as to unduly narrow the range 
of scientific approaches being taken to respond to several agency missions. 
Weather modification is not a well-developed technology. Given the current 
state of the art, the current mechanisms of coordination appear to be appropriate 
and adequate. 71 

A contrary view was stated in the report by the General Accounting 
Office (GAO) on the need for a national program in weather modifica- 
tion research : 

A national program in weather modification research is necessary to effectively 
control activities of the agencies involved. Although this need was recognized as 
early as 1966. the organizations established to coordinate these activities have 
not developed and implemented an effective overall national program. Although 
coordinating groups have tried to develop national programs, their implementa- 
tion has not been successful. The present fragmentation of research efforts has 
made it extremely difficult for agencies to conduct effective field research which, 
in the case of weather modification, must precede operational activities. 72 

In answer to this conclusion of the GAO report that the Federal 
weather modification research program was not effectively coordi- 
nated, the Office of Management and Budget (OMB) replied that: 

The point on ineffective coordination of research projects is not supported by 
fact. Weather modification research is well coordinated by the Interdepartmen- 
tal Committee on Atmospheric Sciences (ICAS). ICAS meets monthly and pro- 
vides members and observers the opportunity to exchange information in a timely 
manner. Interdepartmental coordination of weather modification activities has 
been, in our opinion, achieved through the efforts of ICAS and the member 
agencies in an exemplary manner. 7 '' 

The several means, formal and informal, by which the Federal 
weather modification research program is coordinated, or by which 
advice on agency programs is provided, are identified and discussed in 
the following subsections. 

The Interdepartmental Committee for Atmospheric Sciences (ICAS) 

The principal mechanism for coordination of Federal weather 
modification programs has been the ICAS. Weather modification 
has been a principal concern of the committee since its inception in 
1959, and it was recently stated that the ICAS has spent more effort 
dealing with weather modification than with any other single topic. 74 
This close tie and continued interest by the ICAS on weather modi- 
fication was instilled from its beginning, when it incorporated func- 
tions of an existing interagency weather modification committee. 

In 195s. the National Science Foundation recognized the need for 
a formal interagency coordinating mechanism as part of its newly 

70 Droessler. "Weather Modification : Federal Policies, Funding From All Sources, Inter- 
agency Coordination," 1!*77. p. 14. 

71 Eggers, testimony before House Committee on Science and Technology, Subcommittee 
on the Environment and the Atmosphere. 107(5. pp. 111-112. 

- Comptroller of the United States. "Need for a National Weather Modification Research 
Propnim '* report to the Congress, General Accounting Office, B-133202, Washington, D.C., 
Aug. 23. 1974, p. 23. 

Sawhlll. John C. Associate Director, Office of Management and Budget. In a letter to 
Morton B. Henig, Associate Director, Manpower and Welfare Division, General Accounting 
Office. Sept. 12. 1973. 

74 Todd. Edward P. (Chairman of the Tn t erdepartmental Committee for Atmospheric Sci- 
ences), in testimony at hearings on weather modification before the Subcommittee on the 
Environment and the Atmosphere. Committee on Science and Technologv. U S. House of 
Representatives, June 16, 1976, p. 127. 


assigned statutory responsibilities as weather modification lead agency 
and established an Interdepartmental Committee on Weather Modi- 
fication. A year later the newly established Federal Council for Sci- 
ence and Technology (FCST) considered the need for a committee to 
cover atmospheric sciences; and, upon agreement between the Presi- 
dent's science adviser and the Director of the XSF, the existing Inter- 
departmental Committee on Weather Modification was formally 
reconstituted as the FCST's Interdepartmental Committee for At- 
mospheric Sciences. ICAS held its first meeting September 9, 1959. 75 > 76 

The National Science and Technology Policy, Organization, and 
Priorities Act of 1976 (Public Law 94-282) was^ signed May 11, 1976, 
creating the Federal Coordinating Council for Science, Engineering, 
and Technology (FCCSET) . Under the new law, the ICAS, a subcom- 
mittee of the former FCST. should have ceased to function, since 
the parent council was abolished. Prior to the signing of Public Law 
94-282, however, the FCST Chairman addressed a letter to all FCST 
subcommittee chairmen, indicating that these committees should con- 
tinue their normal activities until such time as a new organizational 
structure for FCCSET could be established and begin to function. 
Subsequently, the FCCSET established several supporting subcom- 
mittees, one of which is the Committee on Oceans and Atmosphere 
(CAO) . The ICAS was formally adopted by the CAO on a temporary 
basis, pending creation of its own subcommittee structure. Conse- 
quently, the ICAS lias continued to hold meetings and published its 
customary annual report, under authority given by the Chairman of 
the CAO. 77 Although the future of the ICAS is uncertain, a recent 
survey indicated that its members favored continuation of an *'ICAS- 
like' ? activity. The committee thus intends to meet and conduct business, 
at a reduced level of activity, until the CAO organization becomes firm 
and is in full operation. 78 

The coordination activities of the ICAS for the Federal weather 
modification research program has been particularly valuable, espe- 
cially since 1968, when the Xational Science Foundation was relieved 
of its lead agency role. Prior to that time the XSF had provided leader- 
ship to the Federal program in a number of ways. Beginning in 1969 
the ICAS has continued the sponsorship of the annual Interagency 
Conference on Weather Modification, which the XSF had initiated 10 
years earlier. This annual conference is a "partial mechanism to pro- 
mote effective communications and a source of shared responsibility 
among the Washington program managers and the field program 
managers." 79 These conferences provide a forum for exchanging in- 

75 Special Commission on Weather Modification. '"Weather and Climate Modification," re- 
port to the National Science Foundation. XSF 66-3, Washington. D.C.. Dec. 20. 1965, p. 131. 

76 A discussion of the history and activities of the Federal Council for Science and Tech- 
nology is found in the following report: Bates. Dorothy M. (coordinator). Interagency Co- 
ordination of Federal Scientific Research and Development : The Federal Council for Sci- 
ence and Technology. Report prepared by the Science Policy Research Division of the Con- 
gressional Research Service for the Subcommittee on Domestic and International Scientific 
Planning and Analysis. Committee on Science and Technology. U.S. House of Representa- 
tives. Committee Print. Washington. U.S. Government Printing Office, 1976. 447 pp. Of spe- 
cial interest in this report is a case history of the ICAS: Morrison. Robert E. The Inter- 
departmental Committee for Atmospheric Sciences : a case history. App. Ln pp. 381-396. 
(Included in the case history is a list of ICAS publications through July 1976.) 

" Federal Coordinating Council for Science. Engineering, and Technology. Committee on 
Oceans and Atmosphere. Interdepartmental Committee for Atmospheric Sciences. National 
Atmospheric Sciences Program : fiscal year 1978. ICAS 21-FY7S. September 1977, 96 pp. 

7S Ibid., p. iii. 

"9 Drossier. Weather Modification: Federal Policies. Funding From All Sources Inter- 
agency Coordination, p. 14. 


formation on progress in past years, plans for the coming year, 
thoughts on future projects, and suggestions on solutions to various 
problems encountered. The annual conferences, under ICAS sponsor- 
ship, beginning with the 11th in 1969, have been hosted, at the request 
of the ICAS, by the NSF and by NOAA. The NSF hosted the 11th 
conference, and XOAA has hosted all of those since, starting with 
the 12th. 

At regular meetings of the ICAS, major weather modification pro- 
grams of member agencies are frequently reviewed through project 
briefings by Washington and field program managers. The ICAS has 
formed standing and ad hoc panels to which are assigned responsibili- 
ties for specific facets of the weather modificaion program. Panels in 
the past have worked on problems such as legislation on weather modi- 
fication, a national plan for the Federal weather modification program, 
and a plan for accelerating progress in weather modification. These 
panels address topics as requested by the parent committee and make 
recommendations to the ICAS for actions as required. Two specific 
ICAS reports have dealt with the subject. 80 ' 81 

Besides formal coordination afforded by the annual conferences, dis- 
cussions at ICAS meetings, and studies undertaken by ICAS panels, 
there is also included an account of the Federal weather modification 
program as an appendix to the annual ICAS report. 82 In the early 
years of the ICAS member agencies reported their funding for the 
general support of atmospheric sciences only in two broad categories, 
meteorology and aeronomy. Beginning with fiscal year 1963 the agen- 
cies began to identify specific funds for weather modification, and this 
information has been included since in the annual ICAS report along 
with brief descriptions of member agency programs. 

It was at the request of the ICAS and with the cooperation of the 
Secretary of Commerce that Federal agencies began to report their 
weather modification research activities to XOAA as of November 1, 
1973. 83 Public Law 92-205 requires such reporting by all nonfederal!}' 
sponsored weather modification projects in the United States and its 
territories. 84 This voluntary reporting by Federal agencies, initiated 
by the ICAS, thus assured that the central source of information on 
weather modification projects in the United States is reasonably 

In its 1971 annual report, the ICAS identified selected major re- 
search projects in weather modification which were designated as na- 
tional projects. 85 These national projects were formulated by the 
ICAS members through combination of agency projects in each of 
seven categories of weather modification assigning lead agency respon- 
sibilities in most cases to that agency with the most significant ongoing 

80 Newell. Homer E. A recommended national program in weather modification. Federal 
Council for Science and Technology. Interdepartmental Committee for Atmospheric Sci- 
ences ICAS report No. 10a. Washington. D.C., November 1966. 93 pp. 

81 Federal Council for Science and Technology. Interdepartmental Committee for Atmos- 
pheric Sciences. ICAS report No. 15a. Washington. D.C., June 1971, 50 pp. 

82 The most recent account is found in the latest ICAS annual report : Federal Coordinat- 
ing Council for Science. Engineering, and Technology. Interdepartmental Committee for 
Atmospheric Sciences. ICAS 21-FY7S. Pp. 87-94. 

83 Federal Council for Science and Technology. Interdepartmental Committee for Atmos- 
pheric Sciences. National Atmospheric Sciences Program : fiscal rear 1975. ICAS 18-FY 75 
Washington, DC. May 1974. n. iv. 

M See earlier discussions on Public Law 92 205 under congressional activities, p. 197. and 
under tbe administration of the reporting program by NOAA. p. 2'.V2. 

Federal Council for Science and Technology. Interdepartmental Committee for Atmos- 
pheric Sciences. National Atmospheric Sciences Program : fiscal year 1972. ICAS report 
No. 15. March 1971, pp. 5-6. 


project (s) within each category. The proposed national projects and 
respective lead agencies were : 

1. National Colorado River Basin pilot project. — Bureau of Recla- 
mation, Department of the Interior : To test the feasibility of apply- 
ing a cloud seeding technology, proven effective under certain condi- 
tions, to a river basin for a winter season to augment the seasonal 

'2. National hurricane modification project. — National Oceanic and 
Atmospheric Administration, Department of Commerce : To develop 
a seeding technology and associated mathematical models to reduce 
the maximum surface winds associated with hurricanes. 

3. National lightning suppression project. — Forest Service, Depart- 
ment of Agriculture : To develop a seeding technology and associated 
physical and mathematical models to reduce the frequency of forest 
fire-starting lightning strokes from cumulonimbus clouds. 

4. National cumulus modification project. — National Oceanic and 
Atmospheric Administration, Department of Commerce : To develop 
a seeding technology and associated mathematical models to promote 
the growth of cumulus clouds in order to increase the resulting natural 
rainfall in areas where needed. 

5. National hail research experiment. — National Science Founda- 
tion : To develop a seeding technology and associated mathematical 
models to reduce the incidence of damaging hailfall from cumulonim- 
bus clouds without adversely affecting the associated rainfall. 

6. National Great Lakes snoio redistribution project. — National 
Oceanic and Atmospheric Administration, Department of Commerce : 
To develop a seeding technology and associated mathematical models 
to spread the heavy snowfall of the Great Lakes coastal region farther 

7. National fog modification project. — Federal Aviation Adminis- 
tration, Department of Transportation : To develop seeding or other 
technology and associated physical and mathematical models to reduce 
the visibility restrictions imposed by warm and cold fogs where and to 
the extent needed. 86 

Although most of these national projects were continued for at least 
a while, some of them failed to materialize, as hoped, as truly national 
projects. Few received the expected interagency support and planning 
effort envisioned; however, in spite of these deficiencies, some were 
pursued by the lead agencies, largely as major single-agency projects. 
The National Hail Research Experiment, conducted by the National 
Science Foundation perhaps came closest to a truly national project 
and. with assistance from other Federal agencies, continued through 
1976. 87 A critique of the national projects in weather modification was 
included in the 1974 report of the General Accounting Office on the 
need for a national program in weather modification research. 88 

In answer to charges that the Federal weather modification research 
effort has been poorly coordinated, a conclusion of various studies that 
have been made, the Chairman of the ICAS recently said, "Within the 
IOAS we have considered coordination as it is defined, namely, har- 

» Ibid. 

Shc discussion of the national bail research project under following section on the pro- 
gram of the National Science Foundation, p. 274 ff. 

^Comptroller General of the United States. Need for a national weather modification 
research program. B-133202, 1974. Pp. 16-22. 


monious action, communication within Government. I submit that,, 
using that definition, the weather modification research program is 
probably as well coordinated as any effort within the Government, with 
the possible exception of programs that are entirely within the purview 
of a single agency. The critics of the ICAS coordination effort, how- 
ever, seem to nave been interpreting coordination as including manage- 
ment ; the ICAS is not a management agent.'' 89 

The National Academy of Sciences/ Committee on Atmospheric Sci- 
ences (N AS/GAS) 

Advice has been provided to the Federal Government through ad- 
visory panels, intensive studies, and published reports on weather 
modification, by the National Academy of Sciences. The Committee 
on Atmospheric Sciences (CAS) was organized under the National 
Research Council of the Academy in 1956, with the stated purpose of 
addressing . . itself to the task of viewing in broad perspective the 
present activities in research and education, the exchange of informa- 
tion and related matters as they affect the status of the field and future 
progress toward a balanced national program in the atmospheric 
sciences, and participation in international programs." 90 

At the request of, and sponsored by, the National Science Founda- 
tion, a conference was organized and conducted by the NAS in 1959, 
in which meteorologists, mathematicians, and statisticians met to ex- 
amine needs in weather modification experiments. The report on this 
Skyline Conference on the Design and Conduct of Experiments in 
Weather Modification, 91 which had been held in the Shenandoah Na- 
tional Park in Virginia, made a strong plea for careful statistical 
design of weather modification experiments, pointing out the need for 
long-term programs, standardization of design, the need for basic 
research in cloud physics, and the requirement for cooperation between 
meteorologists and statisticians. 

In March 1963, the CAS appointed a Panel on Weather and Climate 
Modification, "to undertake a deliberate and thoughtful review of the 
present status and activities in this field and of its potential and limi- 
tations in the future." 92 The Panel was chaired by Dr. Gordon J. F. 
MacDonald and was comprised of 11 Government and non-Govern- 
ment members. The Academy Panel worked closely with the NSF's 
Special Commission on Weather Modification, which had been estab- 
Lished in 1964. Three reports were subsequently published by the Panel,, 
based on in-depth studies which had been undertaken. 

The first of these, "Scientific Problems of Weather Modification," 
appeared in 1964; 03 the second, "Weather and Climate Modification: 
Problems and Prospects," was published in 1966; 94 and the third, 

89 Todd. Testimony before House Committee on Science and Technology, Subcommittee on 
the Environment and the Atmosphere. June 197fi. p. S7. 

90 National Academy of Sciences, National Academy of Engineering. Institute of Medicine; 
National Research Council. Organization and members: 1975-1976. Washington, D.C. Octo- 
ber 1975. P. 81. 

n National Academy of Sciences. National Research Council. Report of the Skyline Con- 
ference on the Design ami Conduct of Experiments in Weather Modification. NAS— NBC Pub- 
lication 742. Washington. D.C, l!tn'). 24 pp. 

92 National Academy of Sciences. National Research Council. Committee on Atmospheric 
Sciences. Weather and Climate Modification: Problems and Prospects. Volume I. summary 
and recommendations. Final report of the Panel on Weather and Climate Modification. Pub- 
lication No. 1350, Washington, D.C, I960, p. vii. 

m National Academy of Sciences. National Research Council. Committee on Atmospheric 
Sciences Scientific Problems of Weather Modification : a Report of the Panel on Weather 
and Climate Modification. NAS NRC Publication No. 1236. Washington. D.C. 1964. 56 pp. 

ot National Academy of Sciences. Publication No. 1350. 1906. In two volumes. 40 + 212 pp. 


"Weather Modification : Problems and Progress," came out in 1973. 95 
In addition to the reports produced by the panel, two other National 
Academy studies were conducted in the 1970's which, in part, addressed 
aspects of weather modification. The Committee on Atmospheric Sci- 
ences surveyed the field in a chapter in its 1971 publication, "The 
Atmospheric Sciences and Man's Needs ; Priorities for the Future." 96 
In 1976 a report was prepared by the Committee on Climate and 
Weather Fluctuations and Agricultural Production of the Board on 
Agriculture and Eenewable Resources. A full chapter is devoted to 
weather modification in this report, entitled "Climate and Food; 
Climatic Fluctuation and U.S. Agricultural Production." 97 

Project Stormfury, a major hurricane modification project of the 
Commerce Department's National Oceanic and Atmospheric Admin- 
istration (NO A A), 98 from its inception has had an advisory panel 
composed of prominent scientists, primarily meteorologists. Currently, 
the panel is appointed by and operates under the auspices of the Na- 
tional Academy of Sciences, Committee on Atmospheric Sciences. 
Members of the Stomfurv Advisory Panel all come from either the 
academic community or from private industry. Not only does the Panel 
review program results and experimental designs and make recom- 
mendations, but it also conducts periodic scientific symposia before 
larger groups. A recent program review was held in September 1977, 
and a report on the review is in preparation. 

The National Advisory Committee on Oceans and Atmosphere 

This advisory committee was created by Public Law 92-125 on 
August 16, 1971, and was to be advisory to both the President and the 
Congress on the Nation's atmospheric and marine affairs and to the 
Secretary of Commerce with respect to the programs of the National 
Oceanic and Atmospheric Administration (NOAA). Among other 
duties, the committee was charged with assessing the status of U.S. 
atmospheric and oceanic activities and with submitting an annual re- 
port of its findings and recommendations to the President and the 
Congress. The Secretary of Commerce was also required, on behalf of 
the executive branch, to prepare comments on the NACOA recom- 
mendations. These comments are appended to each of the annual 
NACOA reports. 

As originally constituted by Public Law 95-125, NACOA included 
25 members, all non-Federal, appointed by the President, who also' 
designated one of the members as chairman and one as vice chairman. 
Each department and agency of the Federal Government concerned 
with atmospheric and marine matters was to designate a senior policy 
official to participate as observer and to offer assistance as required. 
The Secretary of Commerce was to make available such staff, person - 

95 National Academy of Sciences. National Research Council. Committee on Atmospheric 
Science^ Weather Modification : Problems and Progress. ISBN 0-309-02121-9. Washing- 
ton, D.C., 1973. 280 pp. 

98 National Academy of Sciences. National Research Council. Committee on Atmospheric 
£ c .V^ ce ^T£ e . Atmospheric Scien ces and Man's Needs; Priorities for the Future. ISBN 
0-300-01912-5. Washington, D.C., May 1971, pp. 42-61. 

97 National Academy of Sciences. National Research Council. Board on Agriculture and 
Renewable Resources. Climate and Food ; Climatic Fluctuation and U.S. Agricultural Pro- 
duction. ISBN O-309-02522-2. Washington, D.C.. 1976 pp. 131-162 

ps For discussion of Project Stormfury, see p. 296 under weather modification pro-rams 
Of the Department of Commerce. 


nel, information, and administrative services as reasonably required 
to carry out committee activities. The life of NACOA was extended 
and its appropriation authorization was increased successively by 
Public Laws 92-657 and 94-69 of October 25, 1972, and August 16, 
1975, respectively. The 1971 act was repealed, however, by Public Law 
95-63, of July 5, 1977, which effectively disbanded the previous com- 
mittee and established a new NACOA. Although many of the provi- 
sions of the new law were similar to the previous one, the size of the 
committee was reduced from 25 to 18 members, appointed by the 
President .with the stipulation that members must be eminently quali- 
fied in knowledge and expertise in areas of direct concern to the com- 
mittee, that is, in atmospheric- and marine-oriented disciplines. 

Since its inception, the posture of NACOA has been to concentrate 
its studies on those important issues where it can make a significant 
contribution, recognizing that an attempt to review and evaluate every 
program and issue within its purview of responsibility could result 
in treating none of them well and could possibly duplicate what others 
are capable of doing better." Among other important topics, weather 
modification has been the subject of examination, deliberation, and 
comment often throughout the 6 years of NACOA's existence. 

Each of the six NACOA annual reports have contained discussion 
and recommendations on weather modification, which was one of the 
four major topics covered extensively in the first annual report. 1 
NACOA's repeated position has been that there is a need for "a coordi- 
nated Federal effort to support the basic research needed to bring 
weather modification to the point of being an operational tool resting 
on a sound technical base" but that "major gaps remain, largely be- 
cause no one agency has the responsibility for identifying and support- 
ing those areas of basic study needed for further progress along a 
broad front." 2 Specific recommendations of NACOA on the Federal 
weather modification program will be discussed in the following chap- 
ter of this report on studies and recommendations. 3 

Other coordination and advisory mechanisms 

Although overall coordination of the Federal weather modification 
programs has been an ICAS responsibility, there are other panels 
which assist certain agencies in connection with major research proj- 
ects, and there have been various workshops on particular problem 
areas through which interagency consensus has been achieved. The 
NSF Weather Modification Advisory Panel has provided important 
guidance to the weather modification research activities of the NSF. 
The presence of representatives from both the Bureau of Reclamation 
and NOAA, the other agencies with major weather modification pro- 
grams, was designed to assure a high level of coordination. The 
National Hail Research Experiment (NHRE) Advisory Panel of 
the NSF also has had representatives from these two agencies. 
Research proposals received by the NSF are reviewed by the Bureau 

National Advisory Committee on Oceans and Atmosphere. A report to the President nnd 
the Poncrres^. First annual report. June 30. 1972. Washington, D.C., U.S. Government 
Printing Office, p. iv. 
1 Ibid., pp. 19-29. 

: National Advisory Committee on Oceans nnd Atmosphere, a report to the President and 
tt <■ I !ongre88. sixth annual report. June 30, 1977, Washington, D.C., U.S. Government Print- 

lng Office, p. 76. 
See Ch. 6. 


of Reclamation and by NOAA, thus giving a direct input to these 
agencies in the decision process as to whether individual research pro- 
posals are to be funded by the NSF. 4 

The agencies coordinate directly with each other at the working 
level whenever the respective programs may benefit thereby. A close 
coordination mechanism was established, for example, between the 
National Hail Research Experiment (NHRE) of the NSF and the Bu- 
reau of Reclamation's High Plains Cooperative Program (HIPLEX) , 
a useful and practical arrangement in view of the geographical prox- 
imity of the two projects in northeastern Colorado and northwestern 
Kansas, respectively. 5 

During the past few years workshops on various aspects and prob- 
lem areas in weather modification have afforded additional oppor- 
tunity for coordination. In 1975 the National Science Foundation spon- 
sored a symposium/workshop on the suppression of hail as part of its 
National Hail Research Experiment. 6 The NSF also sponsored a major 
workshop on inadvertent weather modification at Hartford, Conn., in 
May 1977. 7 Another recent workshop sponsored by the NSF was 
held in August 1977 at Fort Collins. Colo., on extended space and time 
effects of planned weather modification activities. 8 

Since 1967, the Bureau of Reclamation has conducted nine con- 
ferences as part of its "Project Sky water." dealing with various special 
topics of particular concern to the projects and to planned weather 
modification in general. Some of these Sky water conferences have been 
jointly sponsored with other agencies, in particular, the National 
Science Foundation, and more recent conferences have been conducted 
in a workshop format. Following each conference proceedings have 
been published. The first conference was held at Denver, Colo., in 1967, 
on the subject of physics and chemistry of nucleation. 9 The most recent 
conference was a workshop, held in November 1976, at Vail, Colo., 
on environmental aspects of precipitation management. 10 One day of 
this conference was sponsored jointly with the National Science Foun- 
dation. A tenth Skywater Conference is a workshop scheduled for 
June 1978, at Lake Tahoe, Calif., where the topic will be the Sierra 
Cooperative Pilot Project of Skywater. This conference will follow a 
meeting at the same place, sponsored jointly by the American Meteoro- 
logical Society and the Forest Service of the U.S. Department of Agri- 
culture, on Sierra Nevada mountain meteorology. 

Also of interest as a coordination mechanism was the November 
1975, Special Regional Weather Modification Conference on Augmen- 

4 Eggers. testimony before House Committee on Science and Technology, Subcommittee on 
the Environment and the Atmosphere, 1976, p. 110. 

5 Ibid., p. 111. 

6 National Center for Atmospheric Research, NHRE symposium/workshop on hail and its 
suppression, working group reports. Estes Park. Colo.. Sept. 21-28. 1976. "National Hail 
Research Experiment." technical report NCAR/7100-75/2, November 1975, 130 pp. 

7 Robinson. G. D. (Principal Investigator), inadvertent weather modification workshop. 
May 23-27, 1977. Hartford. Conn., final report to the National Science Foundation, under 
grant No. ENV-77-10186. "Hartford, the Center for the Environment and Man. Inc.." 
November 1977. CEM Report 4215-604. 167 pp. 

s Brown. R>ith J.. Robert D. Elliott, and Max Edelstein (editors). "Transactions of 
Workshop on Extended Space and Time Effects of Weather Modification." Aug. 8-12, 1977, 
Fort Collins. Colo. Goleta, Calif., North American weather consultants, February 1978 
(draft), 279 pp. 

9 U.S. Department of the Interior. Bureau of Reclamation. "Phvsics and Cbpmistrv of 
Nucleation." proceedings ; Skywater Conference I, Denver. Colo., July 10-12, 1967, Denver. 
July 1967. 419 pp. 

10 U.S. Department of the Interior. Bureau of Reclamation. "Precipitation. Man. and the 
Environment ; an Overview of Skywatpr IX Conference," second week of November 1976, 
Vail, Colo., Denver, September 1977, 223 pp. 



tation of Winter Orographic Precipitation in the Western United 
States, sponsored jointly by the American Meteorological Society, the 
Department of Water Resources of the State of California, the 
Weather Modification Association, and the Bureau of Reclamation. 11 

In connection with Project Sky water, the Bureau of Reclamation 
has established a number of advisory boards and panels from time to 
time as the need has arisen. These groups have been composed of both 
Government and non-Government experts. In connection with the 
High Plains Cooperative Project (HIPLEX) , the Bureau of Reclama- 
tion has also established citizens* panels to advise on local problems; 
these groups have included local government officials among other indi- 
viduals. Similar local advisory groups have been planned for the Sierra 
Cooperative Pilot Project and are now being organized. 

Another means of coordination is provided through the joint spon- 
sorship of some Federal research efforts. For example, the weather 
modification simulation laboratory at the Colorado State University, 
funded through the National Science Foundation by three Federal 
agencies, is a facility used in support of a number of Federal projects. 
The National Science Foundation has funded a number of research 
studies which support the major weather modification programs of 
other agencies, particularly those of the Bureau of Reclamation and 
the National Oceanic and Atmospheric Administration. 

A coordination and advisory role has also been played from time to 
time by the committees and panels which have been established to con- 
duct major weather modification policy studies. Notable among these 
groups are the Advisory Committee on Weather Control, established 
by Congress in 1953, and the Weather Modification Advisory Board, 
impaneled by the Secretarv of Commerce to implement requirements 
of the National Weather Modification Policy Act of 1976. 12 

Although not officially sponsored by the Federal Government, a 
forum for coordination and exchange of information on Federal as 
well as non-Federal programs is provided through the meetings and 
the journals of professional organizations. The American Meteorologi- 
cal Society (AMS) has sponsored six conferences specifically dealing 
with weather modification, at which the majority of the papers de- 
livered have been related to Federal research projects and at which 
nearly all of the papers have been based on federally sponsored re- 
search. Exchange of information on Federal projects has also been 
afforded through the medium of AMS journals, particularly the "Bul- 
letin of the American Meteorology Society" and the "Journal of 
Applied Meteorology." Among the various specialized AMS commit- 
tees is the Committee on Weather Modification, concerned with ad- 
vances and priorities in weather modification research, the greatest 
portion of which is supported in the United States by the Federal 
agencies. In addition, specialized conferences on some problem aspects 
of weather modification have been sponsored by the AMS, sometimes 
jointly with various Federal agencies. 

" American Meteorological Society, Abstracts of Special Regional Weather Modification 
Conference: Augmentation of Winter Orographic Precipitation in the Western United 
States Nov 11 13, 1975, San Francisco, Calif. (Cosponsored by the U.S. Department 
Of the Interior. Bureau of Reclamation; State of California, Department of Water Re- 
potirccs ; and the Weather Modification Association, Boston (no publication date), 24H nn. 

12 The purpose, formation, activities, and recommendations of these committees are dis- 
eussed in some detail in various other places in this report. 


The Weather Modification Association (WMA) sj^onsors two pro- 
fessional meetings each year, sometimes jointly with the AMS or other 
professional organizations, and also published the "Journal of 
Weather Modification/' These WMA mechanisms provide additional 
opportunities for coordination of Federal projects as information is 
exchanged among participants, many of whom are employees of Fed- 
eral agencies or of contractors on Federal projects. The organization, 
purposes, and activities of the AMS, the WMA, and other nongov- 
ernmental organizations concerned with weather modification are dis- 
cussed under the section on private organizations in chapter 8 of this 
report. 13 

Weather Modification Ad visory Board 

The National Weather Modification Policy Act of 1976, Public Law 
91-490 of October 13, 1976, requires that the Secretary of Commerce 
"shall conduct a comprehensive investigation and study of the state of 
scientific knowledge concerning weather modification, the present state 
of development of weather modification technology, the problems im- 
peding eli'ective implementation of weather modification technology, 
and other related matters" ; and that "the Secretary shall prepare and 
submit to the President and the Congress * * * a final report on the 
findings, conclusions, and recommendations of the study."' 14 

The Secretary of Commerce responded to these requirements by 
appointing an 18-member non-Federal Weather Modification Advisory 
Board to conduct the study and prepare a report recommending a na- 
tional weather modification policy and a national program of research 
and action to carry out the policy. Members of the Advisory Board, 
with their affiliations, and the charter to the Board from the Secretary 
are included in appendix K. The Board's final draft report is to be 
submitted to the Secretary for her approval and any necessary modifi- 
cations, after which it will be transmitted to the President and the 

Owing to the 1976 Presidential election and change of administra- 
tion in January 1977. and because of procedures required by the Fed- 
eral Advisory Committee Act. the Advisory Board was not officially 
appointed until April 1977. Consequently, much of the 1-year allotted 
time for the study had been lost and it was apparent that the report 
could not be completed by October 13, 1977, as required by Public Law 
94-490. An extension of time, requested by the Secretary, was trans- 
mitted to both houses of the Congress, and a bill providing for such an 
extension was introduced in the Senate, 15 but no action has been taken 
to date, and formal action by the Congress to extend the time for com- 
pletion of the study seems unlikely. Meanwhile, the Advisory Board 
continued its study and report development, planning to deliver its 
report to the Secretary of Commerce by June 30, 1978. Following 
public hearings and receipt of comments from other executive branch 
agencies, it is anticipated that the Secretary will transmit the docu- 
ment to the Congress in the late summer or fall of 1978. 16 

u Sp P d. 389. 

14 Public Law 94-490. Sees. 4 and 5. (The complete text of the law is included in app. I.) 
»S. 1938, introduced Jnly 27. 1077. by Sen. Warren G. Masrnuson. 

18 This tentative schedule for completion and transmittal of the report is based on dis- 
cussions by the Weather Modification Advisory Board at its ninth meeting. Apr. 4, 197S, in 
Washington. D.C. 


The Advisory Board has met formally four times in Washington, 
D.C., and one time each in North Forks, N. Dak.; Boulder, Colo.; 
Champaign, 111.; San Francisco, Calif.; Chicago, 111.; Tulsa, Okla. ; 
Atlanta, Ga. ; and Aspen, Colo. — combining public hearings with 
working sessions. Subpanels and other ad hoc groups of Board 
members have also met numerous times to work on specific aspects of 
the study and to prepare draft sections of the report. At a hearing on 
October 26, 1977, the Chairman of the Advisory Board, Harlan 
Cleveland, briefed the Subcommittee on the Environment and the 
Atmosphere of the House Committee on Science and Technology, re- 
lating activities to date of the Board and submitting for the record a 
discussion paper which summarized the Board's thinking at the time. 17 


Background and regulations 

Public Law 92-205 of December 18, 1971, 18 requires reporting 
of basic information on all nonfederally sponsored weather modifica- 
tion activities in the United States and its territories to the Secretary 
of Commerce. The Secretary is further directed to maintain a record 
of weather modification activities taking place in the United States 
and to publish summaries of such information "from time to time." 

Within the Commerce Department the National Oceanic and 
Atmospheric Administration (NOAA) has administered this pro- 
gram on behalf of the Secretary. Rules for carrying out the provisions 
of this legislation, published in the Federal Register, 19 went into effect 
on November 1, 1972. The rules have since been revised and amended 
twice — on February 15, 1974, 20 to cover safety and environmental 
aspects of field activities and to consider possible interference with 
Federal research projects, and again on July 4, 1976, 21 to modify cer- 
tain reporting procedures. A copy of the rules and regulations cur- 
rently in effect appears in appendix L. In the same appendix are 
copies of the forms and specific reporting instructions to be used for 
submission of required information to NOAA by weather modifica- 
tion operators. 

Reporting requirements include initial, interim, and final reports. 
It is required that NOAA receive the initial report at least 10 days 
prior to the commencement of weather modification activities. The 
rules provide for exceptions whereby this 10-day rule may be waived 
under certain emergencies and also require filing a supplemental report 
if the initial report is subsequently found to contain inaccuracies, mis- 
statements, or omissions or if project plans are changed. The interim 
report is required January 1 of each year (October 1 prior to the 1976 
revision of the rules) unless the project has been terminated prior to 
that date. Upon completion of the project, a final report is due, and, 

17 Weather Modification Advisory P,oard. "A U.S. Policy To Enhance the Atmospheric 
Environment," a discussion paper. Oct. 21. 1977, 29 pp. (Also appeared In record of 
hearing: TVS. Congress. House of Representatives. Committee on Science and Technology, 
Subcommittee on the Environment and the Atmosphere. Weather Modification. 95th 
Cong., 1st sess. Oct. 21, 1977, pp. 20-49. 

18 See appendix I for a reproduction of Public Law 92-205 and see earlier section of this 
chapter under congressional activities for discussion of enactment of this law and those 
enacted since which have extended appropriations authorization through fiscal year 1980. 

19 Federal Register, vol. 37. No. 208. Friday, Oct. 27. 1972. 
^Federal Register, vol. 39, No. 10, Tuesday. Jan. 15, 1974. 
21 Federal Register, vol. 41. No. 113. June 10, 1976. 


until such final report is received by XOAA, the project is considered 
active. 22 

Reporting of Federal activities 

Although not required to do so by Public Law 92-205, as of Novem- 
ber 1, 1973, Federal agencies also began reporting to NOAA their 
experimental activities in weather modification. This procedure re- 
sulted from an agreement obtained by the Secretary of Commerce 
from the responsible agencies at the request of the Interdepartmental 
Committee for Atmospheric Sciences (ICAS) and the Office of Man- 
agement and Budget. Reporting guidelines adopted for Federal 
agencies are similar to those for non-Federal projects, using the same 
data forms; however, Federal entities and employees thereof are ex- 
cepted from criminal penalty to which other operators are subject for 
noncompliance, and no Federal agency is required to furnish infor- 
mation or material whose protection is in the interest of national 
security. With similar reporting of federally and nonfederally spon- 
sored activities, there now exists a central source of information on all 
weather modification projects in the United States. 23 

Summary reports on U.S. weather modification activities 

Since the Secretary of Commerce was given responsibility for col- 
lecting information on weather modification activities and for pub- 
lishing "from time to time" summaries of this information, four such 
summary reports have been prepared by the Environmental Modifica- 
tion Office of NOAA's Office of Environmental Monitoring and Pre- 
diction. The first summary covered reported projects which were active 
some time between November 1, 1972, and March 22, 1973. 24 The second 
report incorporated information published in the first summary and 
extended the period of coverage to include activities reported through 
December 1973. 25 Subsequent reports summarized information on 
ongoing weather modification projects underway during calendar years 
1974 26 and 1975, 27 respectively. The latter two summaries include 
information on Federal as well as non-Federal projects for the com- 
plete calendar years. 

An analysis of the weather modification activities conducted in the 
United States during calendar year 1975 and a preliminary analysis 
of activities during calendar years 1976 and 1977 are found in chap- 
ter 7 of this report. These discussions are based upon the latest weather 
modification summary report published by NOAA 28 and a prelimi- 
nary report on the latter 2 years prepared by Charak. 29 

- Charak, Mason T.. "Weather Modification Activity Reports : Calendar Year 1975." Na- 
tional Oceanic and Atmospheric Administration, Office of Environmental Monitoring and 
Prediction, Rockville. Md., June 1976, pp. 3 and 60. 

23 Charak, Mason T. and Mary T. DiGiulian, "Weather Modification Activity Reports ; 
Nov. 1, 1972, to Dec. 31, 1973." National Oceanic and Atmospheric Administration, 
Office of Environmental Monitoring and Prediction, Rockville, Md.. March 1974, pp. 
1 and D-l. 

24 Charak, Mason T. and Mary T. DiGiulian, "Weather Modification Activity Reports ; 
November 1. 1972. to March 22. 1973.'' National Oceanic and Atmospheric Administration, 
Office of Environmental Monitoring and Prediction. Rockville, Md.. March 1973. 23 pp. 

25 Charak and DiGiulian. "Weather Modification Activity Reports ; Nov. 1, 1972 to 
Dec. 31, 1973," 1974. 40 pp. 

26 Charak. Mason T., "Weather Modification Activity Reports ; Calendar Tear 1974." Na- 
tional Oceanic and Atmospheric Administration, Office of Environmental Monitoring and 
Production, Rockville, Md. March 1975, 37 pp. 

^Charak, "Weather Modification Activity Reports; Calendar Year 1975." June 1976, 
64 pp. 

25 Ibid. 

29 Charak. Mason T.. "Preliminary Analvsis of Reported Weather Modification Activities 
In the U.S. for CY 1976 and 1977." (Submitted for publication in the Journal of Weather 
Modification, 1978.) 


It should also be noted that, as part of its responsibilities as lead 
agency- for weather modification under Public Law 85-510, the Na- 
tional Science Foundation (NSF) began collecting reports on weather 
modification activities on a regular basis in 1966. Two years later, how- 
ever, Public Law 90-407 repealed the powers of the NSF to require 
such reporting. During those 2 years, the Foundation published sum- 
maries of reported activities for fiscal years 1967 and 1968, which were 
included in the 9th and 10th annual NSF weather modification re- 
ports that were submitted to the President and the Congress. 30 From 
September 1, 196S, until December 18, 1971, when Public Law 92-205 
was enacted, no Federal department or agency was authorized to col- 
lect reports on weather modification activities. During this interim, 
pertinent information on weather modification activities of the Fed- 
eral Government and on the status of Aveather modification research 
and technology was published in three weather modification summary 
reports, published at the request of the ICAS by NOAA. 31 This brief 
series ended with the report which covered fiscal year 1973 ; however, 
some of the kinds of information contained in these reports will be 
included in the NOAA summary reports on weather modification 
activities ; such material was first so included in the summary for cal- 
endar year 1975. 32 



In accordance with the mandates of several public laws, or self- 
initiated by the agencies or interagency committees, the executive 
branch of the Federal Government lias undertaken a number of major 
studies over the past 25 years on weather modification policy and/or 
recommended programs for research and development. Some of these 
studies have been performed under contract, others have been con- 
ducted by committees of Federal employees, while a third group were 
carried out by Federal committees or panels composed of non-Govern- 
ment experts. Each of the completed major studies was followed by a 
report which included findings and recommendations. 

The earliest studies were conducted in the early 1950's, largely at the 
instigation of the Department of Defense, at that time the agency with 
the major Federal role in weather modification. The most significant 
study and report of the 1950's was that of the Advisory Committee on 
Weather Control, directed by Public Law 83-256. There was an un- 
usually large number of major studies conducted and reports issued 
during the period from 1965 through 1976. The reports included two 
from the National Academy of Sciences, two from the Interdepart- 

80 National Science Foundation. "Weather Modification : Ninth Annual Report for Fiscal 
Fear Ended June HO, 1967." NSF 68-21. Aug 28. 1968. Washington. D.C.. U.S. Govt. Print. 

Off., Aug. 28, 1968, pp. 75-77 : and . "Weather Modification ; Tenth Annual Report 

for Fiscal Year Ended June 30, 196S," NSF 69-18, Washington. D.C., U.S. Govt. Print. 
Off.. Aug. 1969, pp. 111-115. 

31 U.S. Department of Commerce. National Oceanic and Atmospheric Administration. 
"Summary Report: Weather Modification ; Fiscal Years 1969. 1970. 1971." Office of the 
Assistant Administrator for Environmental Modification. Rockville, Md.. May 1973. 163 pp. : 
. "Summary Report : Weather Modification ; Fiscal Year 1972." Office of Environmen- 
tal Monitoring and Prediction, Rockville. Md., November 1973. 226 pp. : and . "Sum- 
mary Report : Weather Modification ; Fiscal Year 1973." Office of Environmental Monitor- 
ing and Prediction. Rockville. Md.. December 1974. 155 pp. 

32 Cbarak, "Weather Modification Activity Reports ; Calendar Year 1975," June 1976, pp. 


mental Committee for Atmospheric Sciences (ICAS), three from the 
National Science Foundation, and at least one each from the Depart- 
ment of Agriculture, the Environmental Science Services Administra- 
tion (predecessor of XOAA), and the Domestic Council's Subcom- 
mittee on Climate Change. In 1966 alone, at least five reports on 
federally sponsored weather modification studies appeared. The Na- 
tional Advisory Committee on Oceans and Atmosphere (NACOA) 
has also issued policy statements on weather modification in each of its 
six annual reports to date. 

The most recent major study was undertaken in 1977 by the Weather 
Modification Advisory Board under the auspices of the Department of 
Commerce, which has been directed to conduct such a policy study and 
to submit a report to the Congress in accordance with the National 
Weather Modification Policy Act of 1976 (Public Law 94-490). 

The principal weather modification studies and reports, sponsored 
by the executive branch are discussed very briefly in the following sub- 
sections. 33 The conclusions and recommendations of the major policy 
studies are discussed and summarized in a separate chapter of this 
report. 34 

Studies of the early 1950' s 

In 1950, there were controversies among scientists over the validity 
of reported results from weather modification experiments, notably 
Project Cirrus, a Defense Department project, conducted primarly by 
the General Electric Company under contract. 35 It was agreed by those 
involved that there should be an independent scientific review of the 
work and the claims of spectacular results. The appointed review com- 
mittee was organized under the jurisdiction of the Department of 
Defense, since Project Cirrus was sponsored by that Department, with 
Dr. Bernard Haurwitz of New York University as chairman. The 
committee was to investigate results and report to the Defense Depart- 
ment; however, when the report was submitted in the late spring of 
1950, it was classified "confidential," to the dismay of committee mem- 
bers, since it had been hoped that the report would explain the real 
prospects of weather modification to the public. 36 According to Byers, 
the Defense Department finally agreed to let the report be published 
by the American Meteorological Society, and it appeared "in the guise 
of a report requested by the president of the Society." 37 - 38 The overall 
tenor of the report was one of skepticism toward the claims of success 
for Project Cirrus, and the concluding paragraph of the report stated 
that : 

It is the considered opinion of this committee that the possibility of artificially 
producing any useful amounts of rain has not been demonstrated so far if the 
available evidence is interpreted by any acceptable scientific standards. 38 

In view of the potential value of weather modification techniques and 
the controversial results obtained thus far, the research agencies of the 

33 Studies and reports of the congressional support agencies have been noted earlier in 
this chapter under the discussion of congressional weather modification activities. See 
p. 209. 

34 See chap. 6, p. 313 ff. 

85 For a discussion of Project Cirrus, see p. 39, under the history of weather modification 
in chapter 2. 

36 Byers, Horace W., "History of Weather Modification," In Wilmot H. Hess (editor). 
Weather and Climate Modification. New York, Wiley, 1974, pp. 33-34. 

37 Ibid., p. 34. 

38 The report appeared under correspondence, signed by members of the committee, in the 
Bulletin of the American Meteorological Society, vol. 31, No. 9, November 1950. pp. 346-347 

39 Ibid . p. 347. 


U.S. Army, Navy, and Air Force, along with the U.S. Weather Bureau, 
in 1951 appointed an Artificial Cloud Nucleation Advisory Group, 
chaired by Dr. Sverre Petterssen of the University of Chicago. The 
Advisory Group was asked to make a survey of the field of weather 
modification and u . . . to recommend a program for experiments and 
tests that could be expected to clarify major uncertainties that existed 
at that time for the operational uses of weather modification tech- 
niques." The Advisory Group found some support for the claims of 
Langmuir that seeding had affected larger atmospheric systems, but 
emphasized the need for clarification experiments. The group con- 
cluded that there was good evidence to indicate that cold stratus (and 
presumably cold fog) could be dispelled by nucleation. It had not been 
possible in any case to predict what results would have occurred if 
seeding had not been performed, indicating the need for more rigorous 
control of future tests. The Advisory Group consulted a number of 
experts in the field and all agreed that there was need for a coordinated 
program for experiments in order to determine whether or not weather 
systems can be modified with useful results. 40 

The Advisory Group recommended establishment of six projects to 
answer these questions and was requested to remain and furnish advice 
to the projects and their sponsoring agencies, provide for information 
exchange, and review results. One of these projects was sponsored by 
the Weather Bureau, and of the five sponsored by the Defense Depart- 
ment, four were conducted by contractors and the fifth by the Army 
Signal Corps in house. In July 195± the Advisory Group met with 
representatives of all the projects and sponsoring agencies, reviewed 
the results in detail, and recommended that full reports on each proj- 
ect be published. Project results were subsequently reported in a 1957 
monograph of the American Meteorological Society. 41 

Advisory Committee on Weather Control 

The first major comprehensive study of weather modification and 
its ramifications was undertaken by the Advisory Committee on 
Weather Control, following the congressional mandate under Public 
Law 83-256, of August 13, 1953, which established the Committee and 
directed that the study and evaluation of weather modification be per- 
formed. The Committee was comprised of the Secretaries of five de- 
partments and the Director of the National Science Foundation, or 
their designees, and five private members, including the Chairman, 
who were appointed by the President. 42 Chaired by Dr. Howard T. 
Orville, the Committee forwarded its two-volume report 43 to Presi- 
dent Eisenhower on December 31, 1 0r>7, after the June 30, 1956, termi- 
nation date for the act had been extended by Public Law 84—664 of 
July 9. 1950. In its final report the committee recommended : 44 

(1) That encouragement be given for the widest possible competent 
research in meteorology and related fields. Such research should be 

4 Petterssen. Sverre. "Reports on Experiments with Artificial Cloud Nucleation : Intro- 
ductory Note." In Sverre Petterssen. Jerome Spar. Ferguson Hall, Roscoe R. Braham, Jr., 
! lis J. Rattan. Horace R. Byers. H. J. aufm Kampe, J. J. Kelly, and H. K. Weickmann. 
Cloud and Weather Modification: a Group of Field Experiments. Meteorologieil mono- 
hs, vol. 2. No. 11. American Meteorological Society, Boston, July 1957. pp. 2-3. 
Ibid,, 115 pp. 
43 Public Law 83-256, sections 4 and 5. 

Arlvisorv Committee on Weather Control, final report of thp Advisory Committee on 
Wp.itbf>r Control, Washington, D.C., U.S. Government Printing Office, 1958, in two volumes, 
22-422 pp. 

« Ibid., vol. I. pp. vll-viii. 


undertaken by Government agencies, universities, industries, and other 

(2) That the Government sponsor meteorological research more 
vigorously than at present. Adequate support is particularly needed to 
maintain continuity and reasonable stability for long-term projects. 

(3) That the administration of Government-sponsored research pro- 
vide freedom and latitude for choosing methods and goals. Emphasis 
should be put on sponsoring talented men as well as their specihc 

(4) That an agency be designated to promote and support research 
in the needed fields, and to coordinate research projects, it should also 
constitute a central point for the assembly, evaluation, and dissemina- 
tion of information. This agency should be the National Science 

(5) That whenever a research project has the endorsement of the 
National Science Foundation and requires facilities to achieve its pur- 
pose, the agency having jurisdiction over such facilities should pro- 
vide them. 

National Academy of Sciences studies 

The Committee on Atmospheric Sciences of the National Academy 
of Sciences (NAS/CAS) produced its report on the first of two major 
studies on weather modification in 1966. The report, entitled "Weather 
and Climate Modification : Problems and Prospects,'' 45 was prepared 
by the Committee's Panel on Weather and Climate Modification, with 
joint support from the National Science Foundation and the Com- 
merce Department's Environmental Science Services Administration. 
Volume 1 of the report contains a summary of the study and recom- 
mendations, while the second volume presents a general assessment of 
the subject, on which the panel based its conclusions and recommenda- 
tions. The report expressed cautious optimism regarding the future of 
weather modification. Among its recommendations were an increase 
in Federal support from the 1965 level of $5 million to at least $30 
million by 1970 and the early establishment of several carefully de- 
signed, randomized seeding experiments, planned in such a way as to 
permit assessment of the seedability of various storm types. The re- 
port addressed mostly technical and administrative problems; it did 
not consider social, legal, and economic aspects of the subject, since 
these topics were taken up in a concurrent study by the NSF's Special 
Commission on Weather Modification, which worked closely with the 
NAS panel. 46 

The second major study was completed by the Panel on Weather 
and Climate Modification of the NAS Committee on Atmospheric 
Sciences in 1973. 47 Sponsored jointly by the National Science Founda- 
tion and the Department of Commerce, the panel was given respon- 
sibility in the study "(1) to determine the scientific and national prog- 
ress in weather modification since the earlier study of the field was 
reported upon in 1966, (2) to consider future activities that would 

45 National Academy of Sciences. National Research Council, Committee on Atmospheric 
Sciences. Wenther and Climate Modification : Problems and Prospects. Publication No. 1350, 
Washington. D.C., 1966. in 2 volumes. 40+212 pp. 

46 See discussion be^w on reports bv the National Science Foundation, p. 239. 

47 National Academy of Sciences. National Research Council, Committee on Atmospheric 
Sciences, "Weather Modification : Problems and Progress," ISBN 0-309-02121-9, Washing- 
ton, D.C., 1973. 280 pp. 


guide and strengthen work toward further progress, (3) to examine 
and clarify the statistical design and evaluation of modification ac- 
tivities, and (4) to determine the current circumstances bearing on the 
increase, decrease, and redistribution of precipitation." 48 In its report, 
the panel attempted to fufill these objectives and further proposed 
the following three goals for improving the science and technology of 
weather modification : 49 

1. Completion of research to put precipitation modification on a 
sound basis by 1980. 

2. Development during the next decade of the technology required 
to move toward mitigation of severe storms. 

3. Establishment of a program that will permit determination by 
1980 of the extent of inadvertent modification of local weather and 
global climate as a result of human activities. 

Research programs required to achieve these goals were outlined 
along with basic functions to be performed by the several Federal agen- 
cies. These organizational recommendations for the Federal program 
were : " (1) the identification of a lead agency, (2) the establishment of 
a laboratory dedicated to the achievement of the proposed national 
goals, and (3) assignment to the recently established National Advisory 
Committee on Oceans and Atmosphere of the responsibility for examin- 
ing the public policy issues of weather modification, as well as the 
development of organization and legislative proposals."' 50 

Studies by the Interdepartmental Committee for Atmospheric Sciences 

Another report to appear in 1966 was the first of two by the ICAS 
on weather modification, which prescribed a recommended national 
program in the field. 51 Compiled by the chairman of the ICAS Select 
Panel on Weather Modification, Dr. Homer E. Newell of the National 
Aeronautics and Space Administration, the report laid out details for 
such a national program and contained, as appendices, the earlier 
recommended program of the ICAS Select Panel itself, as well as 
recommendations from the concurrent studies by the NAS and the 
NSF Special Commission. 

The ICAS completed another interagency study in 1971, when it 
produced a report which outlines a program for accelerating national 
progress in weather modification. 52 The report attempted to identify 
national weather modification needs and designated research projects 
for meeting these needs as national projects, each with a responsible 
lead agency and support from other Federal agencies. 53 Some of these 
projects were already underway or in planning stages by various 
agencies. Few were ever consummated as truly interagency national 
projects as envisioned, though there was some degree of cooperation 
in some, such as the National Hail Research Experiment (NHRE), 

* 8 Ibid., p. ill. 
*» Ibid., p. xv. 

« Newell, Homer E., "A Recommended National Program in Weather Modification," Fed- 
eral Council for Science and Technology, Interdepartmental Committee for Atmospheric 
Sciences, ICAS Kept. No. 10a, November 1966, 93 pp. 

52 Federal Council for Science and Technology, Interagency Committee for Atmospheric 
Sciences, "A National Program for Accelerating Progress in Weather Modification, ICAS 
Kept. No. 15a. June 1971, 50 pp. „ . 21.. Aa 00 . . 

M For a list of the seven national projects identified by the ICAS, see p. 224. under the 
discussion of the activities of the ICAS. 


and others, such as Interior's Colorado River Basin pilot project 
(CKBPP), continued essentially as large single-agency projects. 

Domestic Council study 

A weather modification study was undertaken in 1974, following 
establishment of a Subcommittee on Climate Change by the Environ- 
mental Eesources Committee of the Domestic Council. Comprised of 
representatives from the Office of Management and Budget (OMB) 
and most Federal agencies with atmospheric sciences programs, except- 
ing the Defense Department, the subcommittee attempted to assess the 
Federal role in weather modification. Drawing upon recent documenta- 
tion on the progress, status, and problems in the field, and through a 2- 
day hearing of representatives from various parts of the weather modi- 
fication community and other interested groups, the subcommittee 
prepared its report in 1975. 54 In its executive summary, the Domestic 
Council report found that : 

Weather modification represents a potential tool for exerting a favorable influ- 
ence over destructive weather events and for augmenting water supplies in some 
areas where additional water is needed for energy, food, and fiber production ; 55 

and the following general recommendation was formulated : 

A policy should be adopted to develop, encourage, and maintain a comprehen- 
sive and coordinated national program in weather modification research and in 
the beneficial application of the technology along the lines of the recommenda- 
tions embodied in this report. 56 

Specific findings and recommendations were also given for each of 
the three areas of research, operations, and regulation, which the sub- 
committee examined. 57 

Policy and planning reports produced by Federal agencies 

Since the very early studies of the 1950-51 era, instigated primarily 
by the Department of Defense, other Federal agencies have undertaken 
major policy and planning studies, either as "in-house" efforts or 
through contractors or committees established by the agency. 

The National Science Foundation has produced the greatest num- 
ber of agency policy reports, based on studies conducted by its Special 
Commission on Weather Modification and by contractors. Two reports 
appearing in 1966 were prepared by or under auspices of the Special 
Commission, culminating a study authorized in October 1963 by the 
National Science Board. 58, 59 The Special Commission, established in 
June 1964 and chaired by Dr. A. R. Chamberlain of Colorado State 
University, had been "* * * requested to examine the physical, 
bilogical, legal, social, and political aspects of the field and make rec- 
ommendations concerning future policies and programs." 60 Phvsical 
aspects were studied in cooperative liaison with the NAS panel in its 
concurrent study ; 61 however, the membership of the Special Commis- 
sion reflected expertise in the other aspects of weather modification not 

64 Domestic Council. Environmental Resources Committee. Subcommittee on Climate 
Change, "The Federal Role in Weather Modification," Washington, D.C., December 1975, 
39 pp. 

55 Ibid., p. i. 

» Ibid. 

w Ibid.. pp. i-iii. 

68 Special Commission on Weather Modification. NSF 66-3. 1966. 155 pp. 

59 Taubenfeld. Howard J. "Weather Modification: Law. Controls. Operations." report to 
the Special Commission on Weather Modification. National Science Foundation, NSF 66-7, 
Washington. D.C.. 1966. 79 pp. 

*> Special Commission on Weather Modification. NSF 66-3, 1966, p. iii. 

61 See p. 237 above. 


previously addressed by the other studies. Much of the background 
work for the treatment of these other aspects of the problem was sup- 
ported by NSF grants and subsequently published as separate reports. 
These included the biological aspects, human dimensions, international 
relations, and legal aspects. Of these separate studies all were published 
in various nongovernmental media, except the last one, which appeared 
in the format of the XSF Special Commission report. 62 All of these 
aspects were reviewed and summarized, and recommendations were 
presented, in the principal Commission report, which sought to answer 
the following question : "With the physical possibility of modifying 
the weather and climate already partly demonstrated, how by artifi- 
cially inducing deliberate changes in the environment may man act to 
control or develop changes in the atmosphere considered to be desirable 
by society ?" 63 

A contracted study was undertaken for the NSF by the Rand Corp. 
in 1962 to establish the framework of a cohesive approach to research 
on weather modification. Part of the program was to conduct a com- 
prehensive state-of-the-art review of the field: however, the appear- 
ance of the 1966 National Academy study 64 negated the immediate ne- 
cessity for such a reexamination. Nearly 3 years later Rand did publish 
such a review, recognizing that there had been "sufficient progre-s in 
the overall field of weather modification research to now warrant a new 
overview." 65 

The authors of the report stressed the following points: "(1) the 
possibility of inadvertent weather or climate modification is rapidly 
becoming a probability, as human effects on the atmosphere and the 
surface of the planet grow at an increasing rate: (2) progress in 
weather modification research continues to be hampered by the preva- 
lent lack of cohesive effort by both theoreticians and experimenters; 
(3) computers of advanced design and increased capacity will handle 
atmospheric models of considerably greater sophistication than in the 
past; and (-1) this is a not-to-be-neglected opportunity for interactive 
research — constant two-way feedback from theory to experiment to 
theory, with dynamic atmospheric models facilitating each advance." 66 
General and specific recommendations concerning what they consid- 
ered to be the most urgently needed research areas and required instru- 
mentation developments were included in the report. 

In 1965, following a request from the Chief of the U.S. Weather 
Bureau, Dr. Robert M. White, the Bureau published an "in-house" 
report on its role in weather modification research. 07 In the report it 
was recognized thai research responsibilities extend beyond considera- 
tion of scientific and technical problems; however, it dealt primarily 
with meteorology, leaving to other ongoing studies the treatment of 
administrative, 'military, international, and ecological aspects, al- 
though some legal and legislative questions were discussed. r,s It was 

02 Taubenfeld, NSF 66-7. „ - m _ _ 

°3 Special Commission on Weather Modification. XSF 66-3. 1966, pp. 7-8. 
•* National Academy of Sciences, publication Xo. 1350, 1966. 

« Staff of the Weather Modification Research Project of the Rand Corn . Weather Modi- 
fication Progress and the Need for Interactive Research." The Rand Corp., memorandum 
RM-5835-NSF. Santa Monica. Calif., October 1968, 88 pp. 

^GdVman Y)onald L., .Tames R. Hibbs. and Paul I,. Lnskin. "Weather and Climate Morti- 
fication," a" report to the Chief. U.S. Weather Bureau. U.S. Department of Commerce, 
Weather Bureau, Washington, D.C, July 10, 1965, 46 pp. 

« Ibid., p. 1. 


made clear that the report was not intended to be statement of policy 
of the Bureau, the Commerce Department, or the Federal Govern- 
ment, but was rather to be considered as a contribution to the national 
discussion of the future direction of weather modification in the United 
States. 69 

Another one of the many studies appearing in 1966 was a report by 
the Commerce Department's Environmental Science Services Admin- 
istration (ESSA), the organization which preceded the present Na- 
tional Oceanic and Atmospheric Administration (XOAA). 70 Prepared 
in response to a request by the ICAS, the report was prepared by an 
"in-house" task group to define an expanded ESSA program in light 
of the recommendations of the XAS Committee on Atmospheric Sci- 
ences Panel on Weather and Climate Modification and those of the 
XSF Special Commission on Weather Modification, which appeared 
in reports that year. 71 ' 72 It outlined a 5-year program of research for 
the fiscal years 1968 through 197:2, with projects ranging from large- 
scale field experiments to those in more basic aspects of atmospheric 
science pertinent to weather modification. 

A report was published in 1968 by the U.S. Department of Agricul- 
ture, as part of the continuing joint research planning by the Depart- 
ment and State agricultural experiment stations. 73 The recommended 
program of research and development in weather modification for 
agriculture and forestry supplemented the national program of re- 
search for agriculture. The proposed program addressed direct modifi- 
cation of the weather and the resulting biological, economic, and so- 
cial consequences of such activity. It was intended to contribute to 
knowledge and technology needed "in the total enterprise of agricul- 
ture and forestry" and to "provide the basis for essential decisionmak- 
ing on weather modification programs affecting nearly every aspect of 
agriculture and forestry. 74 The report discussed national goals, defined 
a national research and development program for agencies of the 
Department of Agriculture and the State agricultural experiment 
stations, and reviewed the necessary research resources, including man- 
power, facilities, and organization. For each major phase of the pro- 
posed research activity, the report recommended levels of Federal in- 
volvement and financial investment for fiscal years 1972 and 1977. 75 

Federal Programs ix Weather Modification 
introduction and fuxdixcr summaries 

e The Federal Government has been involved in weather modifica- 
tion research and development for more than 30 years. As noted ear- 
lier, these research programs are scattered throughout a number of 
Federal departments and agencies. They are not carried out fully in- 
dependent of one another, however, since they are coordinated by man- 

69 Ibid., p. iv. 

70 U.S. Department of Commerce, Environmental Science Services Administration. "An 
Outline of a Proposed 5-Year Plan in Weather Modification," Rockville, Md., April 1966. 
66 pp. 

71 National Academy of Sciences, publication Xo. 1350. 

72 Special Commission on Weather Modification. XSF 66-3. 

7 3 Joint Task Force of the U.S. Department of Agriculture and the State universities and 
land grant colleges. "A National Program of Research for Weather Modification." U.S. De- 
partment of Agriculture. Research Program Development and Evaluation Staff. Washing- 
ton, D.C., January 196S, 3S pp. 

7 * Ibid , p. 1. 
73 Ibid., pp. 6-8. 


agers at the program level, especially through the Interdepartmental 
Committee for Atmospheric Sciences (IOAS). and by scientists and 
engineers at the working level through a number of mechanisms in- 
cluding interagency joint projects and the activities of professional 

The Federal weather modification program has been considered to 
be composed of the several agency programs identified as weather 
modification by the member agencies of the IOAS and reported as 
such to the ICAS. According to the latest IOAS annual report. 7 ' 3 
weather modification programs will be sponsored during fiscal year 
1978 by six departments and agencies: these are the Departments of 
Agriculture. Commerce, Defense, and Interior; the National Science 
Foundation; and the Energy Eesearch and Development Administra- 
tion (part of the Department of Energy as of October 1. 1977) . As late 
as fiscal year 1976 the Department of Transportation also reported a 
program in weather modification, and the National Aeronautics and 
Space Administration (XASA) identified a research program in warm 
fog dispersal through fiscal year 1973. The Environmental Protection 
Agency (EPA) supports research on inadvertent weather change as 
a joint sponsor of the METROMEX project in St. Louis and vicinity. 77 
but does not choose to report this research as weather modification. 

In the early years of the ICAS member agencies reported their fund- 
ing for support of atmospheric science only in the two broad cate- 
gories — meteorology and aeronomy. Beginning with fiscal year 1963, 
however, there has been a discreet identification of funds for weather 
modification; the total Federal effort amounted to $2.7 million that- 
fiscal year. Though there have been occasional dips since then, funding 
for Federal programs has increased steadily to $20.3 million for fiscal 
year 1976; however, planned fiscal year 1978 funds have dropped to 
$17.1 million. 78 

Table 2 summarizes funding for the Federal weather modification 
research program by agency and by research category, as reported to 
the ICAS, for fiscal years 1976 through 1978, data for the latest year 
being estimated. Figure 2 shows the course of funding from fiscal years 
1966 through 1978, from ICAS data assembled by Fleagle, who has 
recently reviewed the history of Federal weather modification funding 
since 1946. 79 From 1946 to 1958 the Federal Government funded several 
extensive field research programs, the Department of Defense provid- 
ing the major support through university and industrial contracts. 
Since expenditures for these programs were not reported under 
weather modification, Federal funding for this period cannot be 
determined. 80 

78 Interdepartmental Committee for Atmospheric Sciences, "National Atmospheric Sci- 
ences Program : Fiscal Year 197S." ICAS 21-FY78, 1977, p. 87. 

77 See discussion of METROMEX under the program of the National Science Foundation, 
p. 38 3 ff. 

78 Federal Coordinating Council for Science, Engineering, and Technology : Committee on 
Atmosnhere and Oceans ; Interdepartmental Committee for Atmospheric Sciences ; "Na- 
tional Atmospheric Sciences Program : Fiscal Year 1978," ICAS 21-FY78, August 1977, 
p. 87. 

70 Fleagle, Robert G.. "An Analysis of Federal Policies in Weather Modification." Back- 
ground paper prepared for the U.S. Department of Commerce Weather Modification Advi- 
sory Hoard, Seattle, March 1977, pp. 6-14. 

80 Ibid., p. 6. 



[In thousands of dollars] 

Fiscal year— 

1976 197T 1977 1978 

Department of Agriculture 

Department of Commerce. 

Department of Defense: 

Army... . 


Air Force 

Department of Interior 

Depa rtment of Transportation 

Energy Research and Development Administration 
National Science Foundation 


Precipitation modification. 

Fop and cloud modification 

Hail suppression 

Lightning modification. 

Hurricane and severe storm modification 

Social, economic, legal and ecological studies 

Inadvertent modification of weather and climate. . 
Support and services. 

70 21 55 20 

6,334 1,146 4,577 5,001 

100 119 268 190 

900 175 221 210 

409 112 550 575 

4,649 1,632 6,446 7,613 


1,086 10 1,155 1,260 

6,216 1,110 5,702 2,250 

20,329 4,589 18,974 17,119 

3,382 1,057 4,881 5,900 

2,164 665 1,906 1,868 

3,080 488 2,950 1,180 

70 21 55 20 

1,961 461 1,911 1,810 

718 135 687 450 

4,834 889 3,693 4,158 

4,120 873 2,891 1,733 

g * . \ I I I I I I | I I I | | 
66 68 70 72 74 76 78 


Figure 2. — The course of Federal weather modification funding (planning budg- 
ets and actual expenditures) from fiscal years 1966 to 1978, as reported by 
the Interdepartmental Committee for Atmospheric Sciences. (Adapted from 
Fleagle, 1977, with latest data from ICAS 21-FY78.) 


In the period 1958 to 1965 the XSF, as part of its lead agency 
responsibilities, reported Federal expenditures in weather modifica- 
tion. Reported expenditures reached about $3 million in fiscal year 

1965, although costs of aircraft, radar, and manpower provided by the 
Defense Department were not identified. Beginning with fiscal year 

1966, expenditures have been reported annually by the ICAS under 
reasonably constant definitions and guidelines. 81 

The general growth in Federal funding between fiscal years 1966 
and 1972 can be seen in figure 2. Fleagle speculates that the funding- 
drop following 1968 could have been a result of research curtailments 
brought on by the Vietnam war or of the failure by the Congress to 
designate a lead agency after that role was taken from the XSF by 
Public Law 90-407. He feels that the resurgence in 1971 and 1972 could 
have resulted from a new emphasis on weather modification, evidenced 
by the endorsement by the Federal Council for Science and Technology 
of seven national projects identified by the ICAS 82 and the appearance 
of a National Academy of Sciences study which emphasized improved 
management and organization. 83 In January 1973 five of the seven 
national projects were suspended or terminated, owing to the exten- 
sive impoundments of appropriated funds by the President. The na- 
tional projects represented about one-half of the total weather modifi- 
cation budget, exclusive of classified Department of Defense expendi- 
tures. The partial recovery through fiscal year 1976 was based on 
increases in the Department of the Interior's Project Sky water, 
XOAA's preparation for resumed hurricane modification research, 
and ERDA's growing research program on the inadvertent effects 
of increased energy generation. 84 

Fleagle notes that "* * * total funding for weather modification has 
improved over the period from 1966 to 1977 largely in response to 
what are perceived as the needs for prompt application of the tech- 
nology," while "reductions have occurred as results of factors external 
to weather modification and external to the agencies." 85 

Table 3 is a summary by agency of Federal weather modification 
research support since fiscal year 1963, excluding inadvertent weather 
modification research. The data were compiled by Corzine of XOAA 
from a variety of sources, which are identified in the table, and were 
accurate as of March 1977. 86 

Changnon compared the Federal weather modification funding data 
with those of the entire Federal research budget. 87 From fiscal year 
1973 to fiscal year 1974, for example, the total Federal research budget 
increased 6.5 percent, and federally sponsored civilian research (non- 
space and nonmilitary) increased 11.8 percent, while weather modifi- 
cation funding dropped 21 percent. Between fiscal years 1969 and 
1973. a period of rapid growth for weather modification support, civil- 
ian research and development increased 120 percent while weather 
modification research increased 87 percent. 

61 Ibid., pp. 6-7. 

S2 See n. 225 for a listing of those national projects. 

83 National Academy of Sciences, National Resenrch Council. Committee on Atmospheric 
Sciences. "The Atmospheric Sciences and Man's Needs ; Priorities for the Future." Wash- 
ington. D.C., May 1971. 88 pp. 

* l Fleagle, "An Analysis of Federal Policies in Weather Modification." 1977. pp. 7-9. 

65 Ibid., p. 9. 

86 Corzine. Harold; in Fred D. White (compiler). "Highlights of Solicited Opinions on 
Weather Modification" (a summary) ; prepared for use by t' e Department of Commerce 
Weather Modification Advisory Board, U.S. Department of Commerce. National Oceanic and 
Atmospheric Administration. Rockville. Md.. March 1977. p. 30. 

87 Changnon, "The Federal Role in Weather Modification," 1977, pp. 17-18. 



1977.) 1 2 

[In millions of dollars] 

Fiscal year 3 






Others < 






0. 96 





















































4. 77 
















6. 66 

5. 50 






3. 77 










4. 70 












1976 (estimate) 


4. 94 


5 1. 12 


16. 37 




5 2.78 







5 2.16 



1 Excludes inadvertent weather and climate modification research funds. 

2 Excludes DOD spending for weather modification operations in Southeast Asia and ?t military airports. 

3 Data based on: 1963-68, NSF Annual Reports on Weather Modification. 1969-71, ICAS Annual Reports 14, 15, and 16. 
1972-76 material collected for Domestic Council Report (figures fcr 1975 and 1976 brought up to date). 1977-78, figures 
submitted to NOAA. 

4 Includes Transportation, EPA, and NASA. 

5 Includes approximately 0.92, 2.18, and 1.56 for thermal modification of warm fog. 

Federal research and development funding for fiscal years 1971 
through 1976, according' to major weather modification research cate- 
gory, is summarized in table 1. which also indicates the agencies under 
whose programs the funds were expended. Changnon notes that these 
data show that: 88 

1. The greatest effort has been in precipitation modification, but with 
a. general decrease in this effort with time; 

•2. There has been a rapid growth of spending on inadvertent modi- 
fication research; 

3. Funding for fog suppression has been decreasing; and 

4. In recent years the research categories receiving the major support 
are precipitation (snow and rain) modification, hail suppression, and 
inadvertent modification. 

1971 THROUGH 1976. (FROM CHANGNON, 1977.) 

[In millions of dollars) 

Fiscal year- 

Type 1971 1972 1973 1974 1975 1976 agencies i 

Precipitation modification 8.0 6.2 6.0 3.7 4.4 5.0 DOC, DOI, NSF. 

Fog and cloud mcdif.cation 2.9 2.9 2.9 2.4 1.1 1 3 DOD, DOT, NSF. 

Hail suppression 2.6 2.9 3.2 3.3 3.5 3.8 NSF 

Lightning modification .9 .7 .7 .7 .2 .1 DOA, DOD, NSF. 

Severe storm modif.cation .8 1.9 1.7 1.5 1 8 2 DOC 

Societal-economic issues .8 .9 1.1 8 6 11 NSF DOI 

Inadvertent. .6 1.7 1.7 2.9 5.2 4.9 NSF', DOT, DOC. 

i DOC = Commerce; DOD = Defense; NSF=National Science Foundation; DOI = Interior ; DOT=Transportation; DOA = 

58 Ibid., p. 18. 


There have been minimal Federal efforts in operational weather 
modification; however, since these activities are usually conducted as 
parts of other operations not considered weather modification, the 
expenditures are difficult to identify. These activities have included 
fog dispersal at airports by the Navy and the Air Force; precipita- 
tion augmentation operations by the Defense Department overseas at 
the request of the Governments of Panama, Portugal, Okinawa, and 
the Philippines; and 1971 efforts to reduce drought in Texas, Okla- 
homa, Arizona, and Florida by the Department of the Interior, the 
Air Force, and NO A A. 89 Shapley reported in 1974 that estimated 
expenditures by the Defense Department between 1966 and 1972 in 
attempts to increase rain during the Southeast Asia war were $21.6 
million. 90 

Federal weather modification programs are summarized, by agency, 
in the following subsections. Included are discussions of the pro- 
grams of the departments and agencies listed in table 2; the Depart- 
ment of Transportation has been included since its program was ter- 
minated so recently. Discussions contain not only those projects which 
are underway or planned for fiscal year 1978, but also activities of 
the recent past, in order to show the continuity and the development or 
phasing out processes for each of the several programs. 



A major weather modification research program has been conducted 
by the Bureau of Reclamation in the Department of the Interior since 
1961. The purpose of this Atmospheric Water Resources Management 
Program, also called "Project Sky water," lias been to develop and ver- 
ify a practical cloud-seeding technology for increasing water supplies 
in the Western States. Initiated through a congressional write-in of 
$100,000 in the fiscal year 1962 Public Works appropriation, the mis- 
sion of the project was simply stated as "research on increasing rain- 
fall by cloud seeding." 91 Congressional direction has been almost en- 
tirely through provisions in Public Works appropriation documents. 
A summary of the appropriation language contained in these docu- 
ments between 1961 and 1977 is found in appendix J. 

Since its inception, the program has been characterized by the fol- 
lowing three guidelines that were established. 92 

1. It was to be an applied research program, using "engineering 
approaches" rather than a basic or pure research program. 

2. Scient ific expertise was to be used where it existed rather than 
from an "in-house" effort. 

3. Additional water and benefits accruing to local groups from re- 
search seeding would not be reimbursed. 

f0 Ibid. 

00 Shaplev. Deborah. "Weather Warfare: Pentagon Concedes 7-year Vietnam Effort," Sci- 
ence, vol. 184. No. 4141. June 7. 1974, p. 1059. 

01 Bureau of Reclamation. U.S. Department of the Interior, "Atmospheric Water Resources 
Management Program ; Project Skywater. Information Summary," presented before the U.S. 
Department of Commerce National Weather Modification Advisory Board, May 31, 1977, 
Washington, D.C., p. 1. 

92 Ibid. 


The Bureau of Reclamation, through Project Skywater, has been 
the principal Federal agency concerned with the operational adapta- 
tion of precipitation enhancement research. 

Recent legislation in the 95th Congress has also enabled the Bureau 
to provide grants to States in order to facilitate emergency weather 
modification activities in hope of mitigating effects of the 1976-77 
drought. This program, not part of the Atmospheric Water Resources 
Management Program, is discussed in a subsequent section. 93 

Table 5 is a summary of weather modification research funding and 
projected funding from fiscal year 1976 through fiscal year 1978 for 
the Bureau of Reclamation. All of the funds shown are associated 
with Project Skywater and do not include those previously mentioned 
in connection with emergency grants for drought alleviation. 


[In thousands of dollars] 

Fiscal year 


Fiscal year 

Fiscal year 





Precipitation management: 

Snow augmentation (including SCPP) 





Rain enhancement (HIPLEX) 

2, 475 

1, 007 

3, 800 

4, 000 

Modeling and comprehensive analysis studies 





Social, economic, legal and environmental 





Support and services 

2 999 


2 1, 376 

2 1, 263 


4, 649 


6, 446 


1 From Federal Coordinating Council for Science, Engineering, and Technology. Interdepartmental Committee for 
Atmospheric Sciences. National Atmospheric Sciences program: Fiscal Year 1978. ICAS 21— Fiscal year 1978. August 
1977, p. 91. 

2 Includes computer and planning costs. 

Project Skywater general discussion 

Over the past decade, the Bureau of Reclamation's Atmospheric 
Water Resources Management Program (Project Skywater) has ac- 
counted for about one-third of the total Federal program in all forms 
of weather modification. All of the Bureau's funding has been directed, 
however, toward research in precipitation enhancement. Of the funds 
appropriated, about 83 percent are used for contracted research. Table 
6 shows the breakdown of funding for the fiscal years 1962 through 
1977 by kinds of contractor and according to in-house or other Fed- 
eral expenditure. From the table it can be seen that 41 percent has 
been allocated to universities, 23 percent to private firms, 10 percent 
to State governments, and 6 percent to other Federal agencies, while 
17 percent has been spent by the Bureau for planning, management, 
and in-house research. Table 7 shows the breakdown of these funds 
in accordance with functions or major projects. The three major 
projects in the table will be discussed briefly below. 

93 See p. 266 of this section, and also see p. 202 under discussion of congressional 



Total incurred 

Fiscal year 





Other Federal 



$70, 000 




83, 747 


100, 000 


133, 000 

42, 000 



459, 630 

$283, 978 

$3, 500 



1,100, 000 



637, 250 

168, 700 

303, 150 

? qpd nnn 

£, JCU, UUU 


1 989 321 

779 125 


368 396 


3,750, 000 


2,717, 689 

859' 000 

345, 000 

423', 311 

286, 200 

4, 631, 200 

1 QfiQ 

o 77R ok 

obit, Idb 

31 MO 

oio, Dty 

4bU, bob 

273, 500 

4, 689, 656 


2, 966, 200 

873, 866 



268, 325 

4, 809, 508 





753, 436 

335, 344 

6, 593, 650 


3, 539, 323 


664, 926 

784, 857 





1, 105, 029 

905, 200 

889, 387 

173, 021 

6, 385, 576 


899, 110 

1,498, 982 

336, 104 

976, 747 

189, 282 

3,900, 225 


768, 911 





3, 997, 224 


497, 572 


617, 133 

1,677, 593 



Transition quarter 

214, 245 

609, 229 

234, 528 


96, 175 

1, 624, 091 

1977 (estimate) 



1,200, 000 


400, 000 

6, 454, 481 


27, 278, 985 

14, 669, 398 

6, 276, 652 

10, 518, 949 

3, 869, 489 

3 62,348, 381 

Percent 44 23 10 17 6 100 

1 Bureau of Reclamation. Atmospheric Water Resources Management Program: Project Skywater. Infcrmaticn summary. 
May 31, 1977, p. 24. 

2 Includes salaries, equipment, supplies, and computer costs. 

3 Official total as corrected for recoveries, underf.nancing, and other adjustments. 

Table 7. — Bureau of Reclamation Atmospheric Water Resources Management 
Program. Allocation of Funding by Function and by Major Projects for Fiscal 
Years 1962 Through 1977 1 

Research and development $31, 749, 665 

Environmental 2, 173, 676 

Associated comprehensive studies 3, 296, 202 

Colorado River Basin Pilot Project 5, 100, 792 

Sierra Cooperative Pilot Project 866, 805 

HIPLEX 10, 557, 767 

Other pilot projects 1, 980, 000 

Planning, management, and program support 6, 623, 471 

62, 348, 381 

1 Bureau of Reclamation, U.S. Department of the Interior. Atmospheric water resources 
management program : Project Skywater. Information summary, May 31, 1977, p. 23. 


Artist's rendering of portable radar used in Project Sky water. (Courtesy of the 

Bureau of Reclamation.) 


Sky water has emphasized cooperation, joint participation, and cost 
sharing with State resource and environmental agencies; and field 
experiments have included research contracted with universities, State 
agencies, and private firms. Funds have also been transferred to other 
Federal agencies, who have cooperated in the various aspects of the 
program. Table 8 is a listing of the principal contractors and Govern- 
ment activities who have participated. Research contracts have been 
concerned with winter orographic snowfall augmentation and in- 
creases in summer convective cloud rainfall — both of which are prin- 
cipal precipitation mechanisms in the Western United States. The 
distribution of major field projects underway or planned during fiscal 
year 1977 as part of Skywater and the locations of contractor institu- 
tions and Federal activities involved in various aspects of the program 
are shown in figure 3. 


University Private Government 

University of Arizona. 

Brigham Young University. 

University of California. 

University of California at Los Angeles. 

University of Colorado. 

Colorado State University. 

University of Denver. 

Fresno State College. 

Harvard University. 

University of Michigan. 

Montana State University. 

University of Nevada. 

New Mexico State University. 

New York University. 

University of North Dakota. 

North Dakota State University. 

University of Oklahoma. 

Pennsylvania State University. 

San Diego State University. 

South Dakota School of Mines and 

South Dakota State University. 
Taft College. 

Texas A. & M. Research Foundation. 
Utah State University. 
University of Washington. 
University of Wisconsin. 
University of Wyoming. 

Amos Eddy, Inc. 

Aeromet, Inc. 

Aerometric Research, Inc. 

Convergence Systems, Inc. 

Colorado International Corp. 

E. Bollay Associates. 

E.G. & G., Inc. 

Electronic Techniques, Inc. 

Enterprise Electronics, Inc. 

Environmental Research and Tech- 
nology, Inc. 

Geophysical Research and Develop- 
ment Corp. 

Human Ecology Research Services. 

M. B. Associates, Inc. 

Meteorology Research, Inc. 

North American Weather Con- 

Stanford Research, Inc. 

T. G. Owe Berg, Inc. 

Travelers Research Inc. 

Weather Science, Inc. 

Western Scientific Services, Inc. 

U.S. Air Force. 

U.S. Army (Pueblo Depot). 

California Department of Transportation. 

California Highway Partol. 

Colorado Department of Natural Resources. 

Colorado River Municipal Water District. 

Forest Service. 

General Services Administration. 

Geological Survey. 

Illinois State Water Survey. 

Kansas Water Resources Board. 

Montana Department of Natural Resources 
and Conservation. 

National Oceanic and Atmospheric 

National Science Foundation. 

Navy Weapons Center. 

Navy Weather Research Facility. 

Nebraska Department of Agriculture. 

North Dakota Weather Modification Board. 

Sacramento River Forecast Center. 

Soil Conservation Service. 

South Dakota Weather Control Com- 

Southwestern Water Conservation District. 
Washington Department of Ecology. 
Texas Water Development Board. 
Utah Department of Water Resources. 

i Bureau of Reclamation. Atmospheric Water Resources Management Program: Project Skywater. Information summary, 
May 31. 1977. p. 26. 

The widespread field projects of Skywater from 1962 through 1977 
are shown in figure 4. In recent years, research experiments and studies 
have been concentrated on three major projects, one of which has 
just been completed, while the other two are in realtively early stages. 
These projects, each of which is discussed below in some detail, are the 
Colorado River Basin Pilot Project, the High Plains Cooperative Pro- 
gram (HIPLEX), and the Sierra Cooperative Pilot Project. In addi- 
I ion lo t he concentrated research effort in these three regional projects, 
the Bureau continues to provide technical planning and equipment 
assistance to local projects in States such as North Dakota, Kansas, 
Texas, and Pi ah. Support is also being given to the development of 
the application of satellite imagery for cloud seeding decisions and 
evaluations and to the adaptation of research cloud models for use in 
local operations. The Skywater Environmental Computer Network 


provides real-time data support to both field research and commercial 
weather modification projects on a cooperative basis. Figure 5 is a 
schematic of the Data Network, with its central unit in Denver, which 
also provides access to real time and archived data for a variety of 
other research projects. Cloud models and other computerized aids are 
made available for testing by winter and summer operators through 
the Environmental Data Network in return for practical appraisals of 
usefulness and recommendations for improvement. 

Planning and other preliminary field studies for possible future 
weather modification cooperative research in the Colorado River 
Basin are continuing. Recently, the final programmatic environmental 
impact statement for Project Skywater was completed. 94 Several site 
specific environmental impact statements, including one for the Colo- 
rado River Basin Pilot Project, were completed earlier. A compre- 
hensive assessment of the entire field of precipitation enhancement is 
being performed, which includes reviews of both research and opera- 
tional project results. 

Project Skywater = FY 1977 

Figure 3.— Major Skywater field projects and locations of contractors and Federal 
institutions during fiscal year 1977. (From Project Skywater information 
summary, May 31, 1977.) 

e * U.S. Department of the Interior, Bureau of Reclamation, "Final Environmental State- 
ment for Project Skywater ; a Program of Research in Precipitation Management, ' Division 
of Atmospheric Water Resources Management, INT FES 77-39, Denver, Oct. 2o, 1977. In 
three volumes. (376 and 316 and 266 pp.) 


Skywater Field Projects 1962-1977 


Figure 4. — Locations of Skywater field projects from 1962 through 1977. ( From 
Project Skywater information summary, May 31, 1977.) 


Research Seeding 
Projects Projects 



Direct Dial Lines To Users 

NWS Observations 

\ / / 

Bureou of Reclamation 

-Data Bank 

2400 Baud High Sped 

■Processed Data 
-Grid Forecasts. 







Figure 5. — Schematic of the Project Skywater Environmental Computer Network. 
(From Project Skywater information summary, May 31, 1977.) 


34-857 O - 79 - 19 


The Colorado River Basin Pilot Project {CRBPP) 

This Avas a large weather modification research project conducted 
by the Bureau of Reclamation under Project Sky water to determine 
the feasibility of augmenting high mountain snowpacks in the San 
Juan Mountains of southwestern Colorado. The seeding and data col- 
lection phase of this large project was conducted between 1970 and 
1975, although planning for the experiment began in 1967. Project 
evaluations were prepared in 1976, and further analyses and environ- 
mental studies are continuing in 1977. The target area selected for the 
CRBPP (or the San Juan Project as it is sometimes called) covered 
nearly 3,400 km 2 (1,300 mi 2 ) of sparsely populated mountainous ter- 
rain east and northeast of Durango, Colo. Elevations extended from 
above 2,750 meters to 4,200 meters. 95 Figure 6 shows the locations of 
target areas and instrumentation arrays in the CRBPP in southwest 

The Colorado River Basin is one of the most water-short areas in 
the Nation, and weather modification has been recommended as a 
practical and immediately available water augmentation technology. 96 
Preliminary results show that a 19-percent augmentation in streamfiow 
may be possible through seeding in this area of headwaters of the 
Colorado River Basin. 97 

05 Aerometric Research, Inc., "Colorado River Basin IMlot Project; Executive Summary 
of Comprehensive Evaluation," prepared for Department of the Interior, Bureau of Reclama- 
tion under contract No. 14-06-D-7332. Goleta, Calif., December 1976, p. 1. 

08 Federal Council for Science and Technology, Interdepartmental Committee for Atmos- 
pheric Sciences, "National Atmospheric Sciences Program : Fiscal Year 1977." ICAS 20- 
FY 77, May 1976, p. 92. 

07 Bureau of Reclamation, "Atmospheric Water Resources Management Program ; Project 
Skywater," May 31, 1977, p. 25. 

Figure 6. — Map showing the locations of target areas and instrumentation 
arrays in the Colorado River Basin Pilot Project in southwest Colorado. (From 
Bureau of Reclamation.) 


Kesults of analyses of the San Juan project indicate that winter oro- 
graphic, storms are somewhat more complex than thought originally, 
but that additional snowpack can be provided through seeding. 
Characteristics of treatable storms have been identified more cleary. 98 
In a major analysis and evaluation of the project it was determined 
that many of the clouds actually seeded in the experiment were not of 
a suitable type, that on some experimental days the weather did not 
develop as forecast, that in some cases seeding material remained in 
the area beyond planned experimental seeding periods, and on some 
days rapid weather changes produced conditions in which precipita- 
tion was decreased by seeding." Consequently, "the total unstratified 
statistical analysis found no difference between precipitation on seeded 
experimental days and control days. However, when days of missed 
forecasts were removed, and data from experimental days were reduced 
to 6 -hour time blocks to improve the correlation between meteorological 
covariates and precipitation, increases during certain classes of seeded 
cases were statistically significant." 1 Nevertheless, the evaluation re- 
port concludes that, "the overall potential for seeding-produced in- 
creases in precipitation during a winter of average snowfall was de- 
termined to be about 10 percent. The resulting potential increase in 
streamflow of about 19 percent is 197 million m 3 for the San Juan 
Kiver." 2 

98 U.S. Department of the Interior, Bureau of Reclamation, "Reclamation in the Seven- 
ties," second progress report. A water resources technical publication, research rept. No. 
28. Washington, D.C., U.S. Government Printing Office. 1!*77. p. 2. 

09 Atmospheric Research, Inc., "Colorado River Basin Pilot Project ; Executive Summary 
of Comprehensive Evaluation," 1976, p. 3. 

1 Ibid. 

2 Ibid. 

Remotely operated cloud seeding generator similar to those used in the Colorado 
River Basin Pilot Project. (Courtesy of the Bureau of Reclamation.) 


The High Plains Cooperative Program {HIPLEX) 

HIPLEX is a comprehensive weather modification research pro- 
gram designed "to develop a practical, scientifically sound, and social- 
ly acceptable technology for precipitation management applicable to 
summer connective cloud systems in the High Plains region of the 
United States." 3 The overall goal of HIPLEX is "to establish a veri- 
fied, effective cloud seeding technology and a policy and management 
background for responsibly producing additional rain in the semiarid 
Plain States. This goal includes improving the current operational 
cloud seeding methods, transferring the techniques and results to con- 
cerned groups ; and enhancing public confidence in their use." 4 

Kesearch in HIPLEX is being conducted at three field sites : Miles 
City, Mont. ; Goocllancl, Kans. ; and Big Spring, Tex. (see fig. 3) . These 
cities represent, respectively, the northern, central, and sourthern 
High Plains ; they were chosen in view of the known or suspected varia- 
tion of climatic conditions and cloud characteristics over the north- 
south extent of the High Plains and the obvious implications of such 
variations on technology transferability. 5 Examination and under- 
standing of the social, political, and agronomic differences across the 
High Plains and their implications for effective technology transfer 
was also instrumental in selecting a variety of field sites. 6 

HIPLEX was initiated in 1973 when the Office of Management and 
Budget (OMB) assigned to the Bureau of Reclamation the responsi- 
bility for mounting an experimental program to test scientific con- 
cepts for augmenting precipitation in the High Plains. The $1 million 
first appropriated for HIPLEX in fiscal year 1974 has grown to about 
$4 million in fiscal year 1977, each recent year's appropriation also in- 
cluding a congressional write-in which has increased OMB's pro- 
gramed budget. 7 About 80 percent of the fiscal year 1977 budget has 
been for contracted research and 20 percent for in-house management 
and support. Universities received 29 percent of the contracted research 
funds, private firms were awarded 81 percent, and 20 percent went to 
State and Federal agencies. 8 Table 9 is a funding breakdown of fiscal 
year 1977 HIPLEX funds by function, expressed in percentage of the 
total HIPLEX budget. 

Table 9. — Fiscal year 1977 HIPLEX funding breakdown by function 

Function : Percent 

Field operations 44. 1 

Analysis 28. 7 

Management, planning, design, data management 22.5 

►Social, legal, and environmental studies (augmentation to State sup- 
ported activities) • 4.7 

Total 100.0 

a Silverman. Bernard A . "HIPLEX : An Overview." Sixth Conference on Planned and In- 
advertent Wenther Modification. American Meteorological Society. Champaign-Urbana, 111., 
Oct 10-18, 1077. p. 311. 

* U.S. Department of the Interior. Bureau of Reclamation, "High Plains Cooperative Pro- 
gram ; Progress and Planning Report No. 2," Denver. March 1976, p. 3. 

G Silverman, "HIPLEX : An Overview," 1977, p. 311. 

6 Ibid. 

7 Ibid. 

8 Ibid., pp. 311-312. 


University of North Dakota radar used under contract in the High Plains Coop- 
erative Program (HIPLEX) of Project Sky water. (Courtesy of the Bureau of 


HIPLEX is envisioned as a 5- to 7-year program, running through 
about 1982. Earliest attention has been given to the site at Miles City, 
Mont., where seeding was first conducted during 1976, though pre- 
liminary studies and measurements of cloud properties have also been 
underway at the other two sites. The following accomplishments should 
be noted : 9 

1. Field facilities and research teams have been established at the 
three field sites : Miles City, Mont. ; Goodland, Kans. ; and Big Spring, 

2. Active participation and cost-sharing with the States is underway. 

3. Major equipment systems have been installed and tested. 

4. Agricultural, economic, and environmental assessment studies are 
underway in all three areas. 

5. Experimental designs and data processing and analysis proce- 
dures have been developed. 

The experimental design for HIPLEX consists of two components — 
an 'atmospheric effort and a socioeconomic and environmental effort. 
Experimental components are divided into three overlapping phases, 
which are consistent with sequential scientific efforts. In a fourth 
phase the developed technology is to be transferred to applicable areas 
in the High Plains region. 10 The details of this four-phase design and 
tentative dates associated with the overall schedule are shown in 
figure 7. 

9 U.S. Department of the Interior, "High Plains Cooperative Program ; Progress and Plan- 
ning Report No. 2," p. 5. 

' 10 Ackerman, Bernice, G. L. Achtemeier, H. Appleman, Stanley A. Changnon, Jr., F. A. 
Huff, G. M. Morgan, Paul T. Schickedanz, and Richard G. Semonin, "Design of the High 
Plains Experiment with Specific Focus on Phase 2, Single Cloud Experiment," Illinois State 
Water Survey, final report on Hiplex design project to Bureau of Reclamation, contract 
14-06-D-7197. Urbana, 111., June 30, 1976, p. 7. 




Phase Atmospheric 

Phase 1 




Phase 2 




Phase 3 
Area Rain 

Phase 4 


• rain characteristics 
•cloud characteristics 

• seeding technologies 
•measurement techniques 
•reasonable hypotheses 

Phase 2 
Modification Hypotheses 


•test of hypotheses 

•field test of seeding 

• develop physical/ 

statistical design 

Sharpen hypotheses and 
select for experiment 

& Environmental 


•political attitudes 
• economic models 
•iegal requirements 
•downwind impact 
•ecological impacts 
•undesirable atmospheric 

Monitor Impacts 




Proof of Concept Experiment: 

Semi-isolated Clouds 
•monitor physical changes 

in clouds 
•monitor precipitation 
• continuous evaluation - 

•conclude when design 

criteria are met 


Phase 3 
Hypothesis Developed 


Monitor Impacts 

Develop physical/statistical 

Launch experiments 
Perform continuous evaluation 
Re-define initial hypothesis 
Conclude when design criteria 




Evaluate Benefits and 

Transfer of Technology 
to High Plains states 
and Other Users 

Figure 7. — Flow of experimental effort in HIPLEX, showing tentative schedule 
through 1991. (From Bernard A. Silverman, 1977, private communication.) 


University of Wyoming instrumented cloud physics aircraft. (Courtesy of the 

Bureau of Reclamation.) 

HIPLEX is primarily a Skywater activity ; however, it also includes 
the integrated research and supporting efforts of State agencies, local 
groups, and other Federal agencies. Field research and analyses are to 
be conducted primarily through contracts with private firms and uni- 
versities, and the project is closely coordinated with related research 
sponsored by the National Science Foundation and the Department of 
Commerce. In order to develop optimum water augmentation poten- 
tial, pertinent State and local organizations in the High Plains have 
joined with the Bureau in planning, funding, and implementing this 
broad research program which is designed to accomplish the 
following : 11 

1. Develop and test more productive seeding methods and evaluate 

2. Resolve the remaining cloud dynamics and precipitation physics 
uncertainties on seeding effects. 

3. Help prepare public weather modification backgrounds and local 
expertise and establish working relations among concerned non-Fed- 
eral entities. 

4. Assess the actual economic value of cloud seeding and the possible 
social and ecological impacts. 

Anticipated overall costs for State cooperation and cost-sharing in 
HIPLEX is estimated to be about $3 million. This contribution 
amounts to 10 to 15 percent of the total HIPLEX research budget, 

11 U.S. Department of the Interior, "High Plains Cooperative Program ; Progress and 
Planning Report No. 2," pp. 3-5. 


since the total Federal portion of the project is projected at about $20 
million. 12 

HIPLEX cooperative agreements for cost-sharing and field research 
support have been negotiated with the States. 13 as shown in table 10. 
Funding provided by some of these States and by the Bureau of Re- 
clamation from fiscal year 1974: through fiscal year 1978 (estimated) is 
shown in table 11. 


Field site States Date signed 

Miles City, Mont Montana... Aug. 25, 1974. 

Goodland, Kans.. Kansas, Colorado, Nebraska May 29, 1974 (tristate). 

Big Spring, Tex Texas Oct. 30, 1974. 


State funds Bureau of 


Fiscal years Kansas Montana Texas Totals funds 

19f4 $6,000 $6,000 $1,250,000 

1975 100,000 $25,000 125,000 1,821,000 

1976 plus transition quarter 100, 000 81, 500 181, 500 3, 482, 000 

1977 100,000 $25,000 65,000 190,000 4,110.000 

1978 (estimate) 100,000 25,000 75,000 200,000 4,000,000 

Total 406,000 50,000 246,500 702,500 14,663,000 

i Private communication from James L. Kerr, Washington representative, Office of Atmospheric Water Resources, Bureau 
of Reclamation. November 1977. 

The Sierra Cooperative Pilot Project (SCPP) 

This cooperative precipitation augmentation research project is 
being initiated under the auspices of Project Skywater and several 
State agencies in the northern Sierra Nevada Mountain Range of 
California and Nevada. Cooperation with commercial cloud seeding 
operators, whose efforts in this region have been funded for several 
decades by west coast utility companies, is expected to be a unique part 
of the project. 

The Sierra project began in 1972 with preliminary planning and 
discussions. Research projects along the crest of the Rocky Moun- 
tains and in the Sierra Nevada have shown the possibility of increased 
snowfall and consequent streamflow enhancement through seeding cer- 
tain types of weather systems. Commercial projects in the Sierra have 
reported consistent 5 to 8 percent streamflow increases. The Sierra 
project is intended to investigate the physical basis for the reported in- 
creases and the feasibility of developing a more precise technology 
for snowfall enhancement for this region. 14 

The Bureau of Reclamation and the State of California agreed to 
pursue a research program in the Sierra Nevada in 1973 and jointly 

™ Ibid., p. 10. 

13 Ibid., p. 9. 

14 U.S. Department of the Interior. Bureau of Reclamation. "A Status Report : The Sierra 
Cooperative Pilot Project "(with excerpts from 'Weather Modification Design for Stream- 
now Augmentation in the Northern Sierra Nevada." an initial study by MAB Associates, 
San Ramon, Calif.), U.S. Government Printing Office, Washington, February 1977, p. 1. 


funded a contract for an assessment of potential environmental effects 
that needed study. Public meetings were held in California and Nevada 
during 1974 to solicit comments on the proposed project. Another con- 
tract, funded in May 1975, led to publication of a project design report 
in December 1976. In August 1975 the California Department of Water 
Resources withdrew as a financial partner in the project, owing to re- 
orientation of priorities and redirection of manpower and funds 
toward other water projects. The department continues to provide 
available information needed for development of the project and mon- 
itors its progress. 

Two studies on likely social and environmental effects of incremental 
snowpack increases on highways and public transportation were com- 
pleted in 1976 by two other agencies of the State of California, the 
California Highway Patrol and the California Department of Trans- 
portation. A survey of individual citizens and organizational repre- 
sentatives on attitudes and concerns about seeding by winter cloud 
seeding was also conducted in 1976. 15 

The preliminary experimental design notes that storms in the Sierra 
cooperative project can be classified into two types and recommends 
that the project should attempt to modify the storm types with sep- 
arate objectives. 

The orographic (westerly) storms should be seeded to increase the efficiency 
of the storm, thus augmenting the amount of precipitation resulting from these 
systems. The procedure would be to seed the storms at light seeding rates to 
avoid overseeding. Seeding would be done with surface seeding generators and, 
under certain circumstances, with airborne seeding generators. 

It was recommended that the convective storms (southerly) be seeded to in- 
crease precipitation at higher, colder elevations, primarily through redistribu- 
tion, providing a greater total precipitation for storage in the snowpack. These 
storms will be seeded heavily, with the object of altering the distribution of pre- 
cipitation with respect to altitude, thus increasing the snowpack. In addition to 
seeding the general orographic background of these storms by surface generators, 
the pilot program would seed the updraft areas of the imbedded convective cells 
heavily with high-output airborne generators. 18 

The specific meteorological hypotheses to be tested by the Sierra ex- 
periment are that : 17 

1. Seeding will increase the average precipitation on treated sample 
events as compared to the untreated events. 

2. Seeding will increase the average elevation of maximum pre- 
cipitation on treated sample events as compared to untreated events. 

3. Seeding will increase the average duration of precipitation and/ 
or the rate of precipitation on treated sample events as compared with 
the untreated events. 

It is intended that the design and evaluation of the SCPP will be a 
continuing process over a period of 7 years, constituting a major 
feature in the step-by-step research in the pilot project. 18 The primary 
hypotheses of the program as well as physical parameters which 
accompany successful or unsuccessful events, will be tested in the 
SCPP evaluation. Basic parameters to be tested statistically are : 19 

1. The average precipitation accumulation. 

2. The elevation of the maximum precipitation band. 

15 Ibid., pp. 1-3. 

16 Ibid., p. 15. 
« Ibid. 

"U.S. Department of the Interior. Bureau of Reclamation. "SCPP Continuing Dosij;n 
Contract." Sierra Cooperative Pilot Project Newsletter. No. 6. May 1977. Denver. Colo., p. 2. 

19 U.S. Department of the Interior, "A Status Report : The Sierra Cooperative Pilot Proj- 
ect," 1977, p. 27. 


3. The average total storm duration, the average duration of pre- 
cipitation during the first and last days of the storm, and the average 
rate of precipitation. 

The regions that are expected to be affected in the Sierra project 
are shown in figure 8. Region 1 is the primary area of effect ; region 
2 is the downwind area recommended for monitoring extra- area effects ; 
and region 3, situated below 1,220 meters (4,000 ft.) elevation in the 
American River basin, is intended to provide real-time precipitation 
data as input for the declaration of an experimental unit and to 
provide better definition of the precipitation distribution within the 
drainage basin. 20 









MT S. /\\ 





* > 






Figure 8. — Map of the Sierra Cooperative Pilot Project region, showing the three 
geographical areas in the project (see text). (From Bure iu of Reclamation, 
Sierra Cooperative Pilot Project, status report, February 1977.) 

2U Ibid., pp. 24-25. 


The planning and design phase of the Sierra project continues, and 
during the winter of 19 f 6-77, field tests were conducted that were 
necessary for design of field operations. During the 1977-78 winter sea- 
son collection of field data under prerandomized seeding conditions 
should be completed ; operating procedures will be tested and refined ; 
equipment will be installed, tested, and calibrated; concepts for co- 
ordinating with operating programs in the area will be developed; 
transport and diffusion studies will continue; and changes in design 
will continue as a result of the increased knowledge acquired from the 
research of the previous year. 21 If the preceding activities have been 
accomplished successfully and weather conditions permit, randomized 
seeding will begin in the 1978-79 season. From historic storm patterns 
it has been estimated that 5 to 7 years of randomized seeding will be 
necessary to obtain a data base suitable for confirmation of the ex- 
pected increases at a significant level. During this period monitoring 
programs and environmental studies will be designed and implemented. 
There will be continued dialog with concerned officials and the general 
public in the project area, and hopefully many answers will be ob- 
tained tu societal, economic, and environmental questions. 22 

Drought mitigation assistance 

Drought emergency relief was requested by the Governors of a num- 
ber of Western States during the summer of 1971. In partial response 
to this request, the President's Office of Emergency Preparedness di- 
rected the Bureau to conduct emergency precipitation stimulation 
operations in Arizona, Oklahoma, and Texas. Skywater personnel 
have also provided scientific consulting services for rain augmentation 
programs in Lebanon, Brazil, India, Tasmania, and Jamaica. 23 

A recent program, not part of Project Skywater, was administered 
by the Bureau of Reclamation, under which grants were given to 
States to support weather modification activities undertaken to miti- 
gate impacts of the 1976-77 drought. Temporary authorities to the 
Secretary of the Interior to facilitate various emergency actions were 
provided by Public Law 95-18, amended by Public Law 95-107, 
enacted April 7, 1977, and August 17, 1977, respectively. Authority 
was granted to appropriate $100 million for a program which included 
short-term actions to increase water supplies. Funds made available 
were to be used to repair, replace, or improve affected water-supply 
facilities and to establish a water bank of available water for rehabili- 
tation. The Bureau implemented the act, publishing rules for emer- 
gency loans, grants, and deferrals under the Emergency Drought Act 
of 1977 in the Federal Register. 24 Procedures were established under 
.sections 423.18 and 423.20 of these rules for State water resource agen- 
cies to apply for nonreimbursable funds for studies and other actions 
to augment water supplies. Bequests wore received during the period 
of availability from six States for funds to support weather modifica- 
tion activities. Table 12 shows the amount of funds approved for each 
State for weather modification projects under this provision. 25 

21 Ibid., p. 47. 

22 Ibid. 

23 Kahan. Archie M.. testimony in : U.S. Congress. House of Representatives, Committee 
on Science and Technology. Subcommittee on the Environment and the Atmosphere. "Weath- 
er Modification." hearings. 04th Congress. 2d session, June 15-18, 1977. Washington, D.C., 
U.S. Government Printing Office. 1976. p. 194. 

■* Federal Register, vol. 42, No. 72. Thursday, Apr. 14, 1977, pp. 19609 -19613. 
^ Private communication from James L. Kerr. Washington Representative, Office of At- 
mospheric Water Resources, Bureau of Reclamation, November 1977. 


Table 12. — Funds provided for States for weather modification- projects by the 
Bureau of Reclamation, under provisions of the Emergency Drought Act of 

Colorado $600,000 

California 300,000 

Kansas 300,000 

Nevada 232,720 

North Dakota 186,133 

Utah 553, 500 

Total 2, 172, 353 


Introduction and general 

Under its Research Applied to National Needs (RANN) program, 
the National Science Foundation (NSF) has in recent years developed 
improved capabilities to stimulate research efforts immediately and 
directly related to problems of society. This program, which dealt pri- 
marily with problem-oriented research, focussed scientific and tech- 
nological resources on selected problems of national importance in an 
attempt to assist in their solution in a timely and practical manner. 
RANN's areas of emphasis included the major category of environ- 
mental programs, under which most of the NSF-sponsored research 
in weather modification had until recently been located. 26 

The NSF program in weather modification supports a broad range 
of research, extending across the disciplines of economic, social, politi- 
cal, legal, environmental, mathematical, and physical sciences. 27 The 
overall goal of the program is "to establish the concept of weather 
modification as a tool to help fulfill societal needs,-' and, to accomplish 
this goal, the program supports research on the following five program 
objectives: 28 

1. To establish the feasibility of, and improve the technology for, 
mitigating the undesirable effects of selected weather hazards. 

2. To delineate the cause, extent, and impact of inadvertent weather 
modification and to subsequently develop ways to use land and energy 
resources to achieve more desirable responses in weather and climate. 

3. To develop an improved capability to design, perform, and evalu- 
ate weather modification experiments. 

4. To investigate the impact of weather modification on society. 

5. To develop specific applications of weather modification to in- 
crease agricultural production. 

Table 13 is a summary of weather modification research funding and 
projected funding from fiscal year 1976 through fiscal year 1978 for the 
National Science Foundation. 

26 In the reorganization of the RANN Directorate in the NSF to the Applied Science and 1 
Research Applications (ASRA) Directorate, effective February 1978, the NSF weather modi- 
fication program was transferred to the basic research Astronomical, Atmospheric, Earth, 
and Ocean Sciences (AAEO) Directorate. Division of Atmospheric Sciences. 

27 Downie. Currie S. and Richard A. Dirks, National Science Foundation weather modi- 
fication program, papers presented at the second WMO Scientific Conference on Weather 
Modification, Boulder, Colo., Aug. 2-6, 1976. World Meteorological Organization, Geneva, 
Switzerland, p. 557. 

28 Ibid. 




[In thousands of dollars) 

Fiscal year— 





Precipitation modification 




Fop and cloud modification 



Hail suppression 

3, 081 




Social, economic, lepal, and environmental 





Inadvertent modification 





Support and services 







5, 702 


1 From Federal Coordinating Council for Science, Engineering, and Technology. Interdepartmental Committee for Atmos- 
pheric Sciences. ICAS 21— fiscal year 1978, p. 94. 

2 Includes technology assessment of hail suppression. 

The RANN weather modification program dealt with a number 
of specific, critical research topics and was dedicated to development of 
improved technology in support of societal needs, transfer of this tech- 
nology to potential users, and exploration of the impac f of weather 
modification on society ; however, the program is not all encompassing. 
In addition to the RANN-supported research, the NSF supported 
weather modification through its basic research program in meteorol- 
ogy and through the atmospheric research facilities at the National 
Center for Atmospheric Research (NCAR) at Boulder, Colo. 29 

The NSF weather modification program is coordinated with weather 
modification programs of other Federal agencies through the Inter- 
departmental Committee for Atmospheric Sciences (ICAS) Panel on 
Weather Modification and through numerous and frequent contacts 
with representatives of the other Federal agencies. In 1975 an NSF 
Weather Modification Advisory Panel was formed, composed of rep- 
resentatives from the Department of the Interior (Buearu of Reclama- 
tion), the Department of Commerce (National Oceanic and Atmos- 
pheric Administration) , the academic community, commercial weather 
modifiers, and industry. The Panel was formed to provide technical 
advice to the NSF program manager for weather modification and to 
assist in coordinating the program with other agencies. 30 As part of the 
concerted effort throughout the executive branch to eliminate advisory 
panels, the NSF Weather Modification Advisory Panel was recently 

Public Law 85-510 of July 11, 1958, directed the NSF "to initiate 
and support a program of study, research, and evaluation in the field of 
weather modification." 31 The Foundation promptly responded in es- 
tablishing the new program, then within its broader program for at- 
mospheric sciences, and expended $1,141,000 for research and evalua- 
tion in weather modification in fiscal year 1959. 32 In designing the pro- 
gram the advice and assistance of outstanding scientists and engineers 
were sought, and an Advisory Panel for Weather Modification was ap- 

20 Ibid. 

30 Federal Council for Science and Technology, Interdepartmental Committee for Atmos- 
pheric Sciences, ICAS 20-FY77. n. 9. r >. 

31 See earlier section of this chapter for discussion of this and other Federal legislation 
on weather modification. 

32 National Science Foundation, "Weather Modification"; first annual report for fiscal 
year ended June 30, 1959, NSF 60-24, p. 3. 


pointed. In an early report to the Director of the NSF, the Chairman 
of the Advisory Panel, Dr. Reuben G. Gustavson, stated : 33 

Placing this important field of research under the aegis of the National Science 
foundation has given rise to a new hope and confidence that the instability fac- 
ors in regard to size and time of support will be removed. This is already bring- 
ng young imaginative workers into the field. The rate of advance will to a large 
neasure depend upon the quality of the trained scientists attracted to the prob- 
.eni. If good scientists are to be attracted into the program, the Foundation must 
be particularly concerned about the financial stability of the program. 

The effect of Public Law 85-510 was to make the NSF the Federal 
lead agency in weather modification, since there were research pro- 
grams underway in a number of other agencies. Historically the NSF 
program has provided the largest measure of Federal support to all 
aspects of weather modification research over the years since establish- 
ment of its program. When Public Law 90-407 of July 18, 1968, 
amended the National Science Foundation Act of 1950, the specific 
mandate for NSF to support a weather modification program and the 
attendant lead agency role were effectively repealed. The further re- 
quirements, established earlier by Public Law 85-510, that activities 
in weather modification in the United States be reported to the NSF 
and that the Foundation should publish an annual report to the Con- 
gress, were also terminated with the passage of Public Law 90-407. 
During the years when NSF was lead agency for weather modification, 
10 annual reports were published, the last one covering fiscal year 
1968. 34 

Following passage of the 1968 law, the NSF continued to support 
basic and applied research in weather modification under the broad 
authority of the National Science Foundation Act of 1950 as amended 
by Public Law 90— 1-07. About one-third of the total Federal support 
for weather modification has been provided by the NSF. 

When the Research Applied to National Needs (RANN) Direc- 
torate was established within the Foundation in 1971 "to bring the 
resources of science and technology to bear on selected important na- 
tional problems, 5 ' 35 most of the weather modification research was 
transferred from the basic atmospheric science program to RANN. 
While nearly all of this research was managed under RANN 
by the Division of Advanced Environmental Research and Tech- 
nology, two major studies were sponsored by RANN's Division 
of Exploratory Research and Technology Assessment, which "sup- 
ports research and assessment to provide greater visibility to the longer 
range social, environmental, and economic impacts of new technology 
applications and to identify and analyze emerging national problems 
that may be avoided or ameliorated by science and technology." 36 

The first of these two technology assessment studies was initiated in 
1971 in response to a request from the Interdepartmental Committee 
for Atmospheric Sciences (ICAS) to explore the feasibility of apply- 
ing technology assessment concepts to planned weather modification 
operational projects. ICAS suggested that the first project for such a 
technology assessment might be the planned project of the Bureau of 

33 Itrd. 

34 National Science Foundation. "Weather Modification: Tenth Annual Report for Fiscal 
Yenr Ended June 30, 1968." NSF 69-18. U.S. Government Printing Office, Washington, D.C., 
1969. 141 pp. 

30 National Science Foundation. "Twentv-sixth Annual Report, for Fiscal Year 1976," 
NSF 77-1. Washington D.C.. U.S. Government Printing Office. 1977. p. So. 

36 National Science Foundation. "Guide to Programs : Fiscal Year 1978," Washington, 
DC, U.S. Government Printing Office, 1977, p. "51. 


Reclamation to augment the flow of the Colorado River by seeding 
orographic clouds to increase snowpack in the Upper Colorado River 
Basin, since the pilot experiment was already underway in the San 
Juan Mountain Range and the Secretary of the Interior needed in- 
formation to make a decision on implementation in the near future. 37 
The contract for the assessment was funded and monitored by NSF, 
the Stanford Research Institute being selected to undertake the study, 
with assistance from the University of California at Davis and a num- 
ber of consultants. The final report was published in 1974. 38 

The second major study was an extensive technology assessment of 
hail suppression in the United States. This project was initiated in 
August 1975 and became known as the Technology Assessment of 
the Suppression of Hail (TASH). The NSF grant was to the Univer- 
sity of Illinois; however, a number of other institutions and individ- 
uals were involved in the study through subcontracts or consulting 
agreements. Total funding for the 18-month project included $290,500 
from NSF and $60,000 from the State of Illinois. 39 The final report 
of the TASH study was published in April 1977. 40 

Table II is a listing of awards in weather modification research by 
the Division of Advanced Environmental Research and Technology 
for fiscal year 1973 through the 1976 transition quarter. The XSF 
weather modification program has been divided into five major areas 
under which the numerous research projects have been categorized. 
These areas, corresponding to the five program objectives stated 
earlier, are : (1) weather hazard mitigation studies on such phenomena 
as hail, thunderstorms, lightning, and tornadoes and an attempt to 
prevent or lessen damage from such storms; (2) weather modification 
technology development ; designed to improve methods for modifying 
the weather and of evaluating results of weather modification efforts; 
(3) inadvertent weather modification investigations to delineate the 
cause, extent, and impact of urban-industrial influences, such as heat, 
moisture, aerosols, and surface roughness, on the weather; (I) socie- 
tal utilization activities which relate the impact of weather on man. 
provide goal orientation, and achieve the societal interface for suc- 
cessful weather modification applications; and (5) an agricultural 
weather modification program which includes developing techniques 
for exerting influence on agricultural systems at critical points during 
the planting, growing, and harvesting seasons in order to expand agri- 
cultural production. 41 Each of these major program divisions will be 
discussed in the following sections. 

37 Weisbecker. Leo W. (compiler). "The Impacts of Snow Enhancement; Technology 
Assessment of Winter Orographic Snowpack Augmentation in the Upper Colorado River 
Basin." Norman, Okla., University of Oklahoma Press, 1974, p. v. 

w Ibld., 024 pp. (A summary of the report was also published separately: Weisbecker. 
Leo W.. "Snowpack. Cloud Seeding, and the Colorado River ; Technology Assessment of 
Weather Modification." Norman, Okla.. University of Oklahoma Press. 1974*. 80 pp.) 

39 Changnon. Stanley A., Jr.. Ray Jay Davis. Barbara C. Farhar. J. Eugene Haas. J. Lore- 
ena Ivens. Martin V. Jones. Donald A. Klein. Dean Mann, Griffith M. Morgan. Jr.. Steven T. 
Sonka. Earl R. Swanson. C Robert Ta.vlor. and Jon Van Blokiand "Hail Suppression ; Im- 
pacts and Issues." Urbana. 111.. Illinois State Water Survey. April 1977. pp. i-iii. 

40 Ibid.. 432 pp.. (A summary of the report was also published in 1977: Farhar. Bar- 
bara ('.. Stanley A. Changnon. Jr.. Earl R. Swanson, Ray J. Davis, and J. Eugene Haas, 
"Hail Suppression and Society," Urbana, 111.. Illinois State Water Survev, June 1977, 
2:3 pp.) 

41 Federal Council for Selenee and Technology, Interdepartmental Committee for Atmos- 
pheric Sciences, ICAS 20-FY77. p. 95. 


Table 14 —Summary of Weathe- Modification Research Awards by NSF/RANN for Fiscal Year 1973 through 1976 Transitional 
Quarter. (Data from Annual Summaries of Awards, RANN, Division of Advanced Environmental Research and Tech- 

Principal investigator/ 


Effective date 




Firor, John W., National Center for 
Atmospheric Research, Boulder, 

Jayaweera, K.O.L.F., University of 
Alaska, College, Alaska. 

Sikdar, Dhirendra N., University of 
Wisconsin-Madison, Madison, 

Boone, Larry M., Department of 
Agriculture, Wash ngton, D.C. 

Taubenfeld, Howard J., Southern 
Methodist University, Dallas, Tex. 

Haas, J. E., University of Colorado, 
Boulder, Colo. 

Corrin, Myron L., Colorado State 
UnrVersity, Fort Collins, Colo. 

Grant, Lewis 0., Colorado State Uni- 
versity, Fort Collins, Colo. 

Barchet, Wm. Richard, University 
of Wisconsin-Madison, Madison, 

McQuigg, James D., University of 
Missouri-Columbia, Columbia, Mo. 

Corrin, Myron L., Colorado State Uni- 
versity, Fort Collins, Colo. 

Warburton, Joseph A., Desert Re- 
search I nstitute, Reno, Nev. 

Hobbs, Peter V., University of Wash- 
ington, Seattle, Wash. 

Veal,' Donald L., University of Wyo- 
ming, Laramie, Wyo. 

Changnon, Stanley A. University of 
Illinois-Urbana, Urbana, III. 

Steele, Roger L., Desert Research 
I nstituta. Reno, Nev. 

Plooster, Myron N., University of 
Denver, Denver, Colo. 

Changnon, Stanley A., Jr., University 
of Illinois-Urbana, Urbana, III. 

Peterson, D. F., Utah State Univer- 
sity, Logan, Utah. 

Weickmann, Helmut K., National 
Oceanic and Atmospheric Admin- 
istration, Boulder, Colo. 

Moore, Charles, B., New Mexico 
Institute of Mining and Technolo- 
gy, Socorro, N. Mex. 

Braham, Roscoe R., Jr., University 
of Chicago, Chicago, III. 

Chessin, Henry, State University at 
Albany, Albany, N.Y. 

Uthe, Edward E., Stanford Research 
Institute, Menlo Park, Calif. 

Klein, Donald A., Colorado State 
University, Fort Collins, Colo. 

Auer. August H., Jr., University of 

Wyoming, Laramie, Wyo. 
Ochs, Harry T., Ill, University of 

Illinois-Urbana, Urbana, III. 


Anderson, C. E., University of 

Auer, August H. 

University of 

Contract for the management, opera- Aug. 1, 1972 12 $2,700,000 

tion, and maintenance of the Na- 
tional Center for Atmospheric Re- 
search (funds for national hail re- 
search experiment program). 

Prevention of ice fog formation by ; n- Sept. 1, 1972 12 17, 600 

ducing cloud cover— Feasibility 
study in Fairbanks. 

Study of the features and energy Oct. 1, 1972 12 96,900 

budgets of northeastern Colorado 

Economic and institutional con- Oct. 15, 1972 12 65,000 

siderations of suppressing hail. 
Study group on the societal conse- Nov. 1, 1972 12 64,400 

quences of weather modification. 
A comparative analysis of publicsup- Dec. 1, 1972 20 60,700 

port of and resistance to weather 

modification projects. 
Heterogeneous ice nuclei. .. do 12 49,800 

Precipitation augmentation from Jan. 1, 1973 12 281,400 

orographically induced clouds and 
cloud systems. 

Precipitation process modification Feb. 15, 1973 12 55, 600 

through ice nucleus deactivation. 

Weather modification management do 12 42,000 


Laboratory cloud simulation to sup- Mar. 1, 1973 12 112,600 

port weather modification research 
and field programs. 

Silver iodide seeding rates and snow- do 12 80,100 

pack augmentation. 

Physical evaluation of cloud seeding Apr. 1, 1973 15 182,000 

techniques for modifying orogra- 
phic snowfall (the Cascade project). 

Development of leaf-derived ice do 12 70,000 

nuclei for weather modification. 

Design of a hail suppression experi- do 12 142,200 

ment in Illinois. 

Sequence effects of heterogeneous Apr. 15, 1973 12 71, 000 


M.crophysics— Diffusion interaction do 39,900 

in ice nuclei plumes. 

Studies of urban effects on rainfall do 12 211,400 

and severe weather. 

Workshop on inadvertent weather May 1, 1973 12 29,900 


Installation and maintenance of May 22, 1973 6 39,033 

ground network for national hail 
research experiment. 

Origin and role of electricity in clouds. June 1, 1973 12 170, 800 

Inadvertent weather modification in do 12 275,000 

the St. Louis area. 

Development of cloud seeding tech- do 12 33, 500 

nology utilizing modified silver 
iodide structures. 

Lidar— Radiometric study of urban do 12 54,100 

atmospheric processes related to 
climatic modification. 

Microbiological impacts of silver July 1, 1973 12 67,600 

iodide used in weather modifica- 

Modification of convective cloud do 12 61, 300 

activity by an urban area. 
2-dimensional cloud modeling— July 1, 1972 12 117,700 

Application to urban effects on 


Study of the features and energy Oct. 1, 1973 12 100, 000 

budgets of northeastern Colorado 

Modification of convective cloud Apr. 1, 1974 12 132,000 



Table 14. Summary of Weather Modification Research Awards by NSF/RANN, for Fiscal Year 1973 through 1976 Transitional 
Quarter, (Data from Annual Summaries of Awards, RANN, Division of Advanced Environmental Research and Tech- 
nology.)— Continued 

Principal investigator/ Duration 

institution Title Effective date (months) Amount 

FISCAL YEAR 1974 AWARDS— Continued 

Barchet, William R., University of Precipitation process modification Feb. 15, 1973 

Wisconsin. through ice nucleus deactivation. 
Boone, Larry M., U.S. Department Economic and institutional consid- Oct. 1, 1973 

of Agriculture. erations of suppressing hail. 
Braham, Roscoe R., Jr., University Inadvertent weather modification in Apr. 1, 1974 

of Chicago. the St. Louis area. 
Changnon, Stanley A., Jr., University Studies of urban effects on rainfall do 

of Illinois. and severe weather. 

Design of a hail suppression experi- June 1, 1973 

ment in Illinois. 

Chessin, Henry, State University of Development of cloud seeding tech- do 

N.Y. nology utilizing modified silver 

iodide structures. 

Chisholm, John P., Sierra Nevada An accurate and inexpensive air- July 1, 1974 

Corp. borne windfinding system. 
Corrin, Myron L., Colorado State Heterogeneous ice nuclei develop- Oct. 1, 1973 

University. ment. 
Davis, Briant L., South Dakota Chemical complexing of silver iodide- Sept. 1, 1972 

School of Mines and Technology. alkali iodide aerosols prepared for 
cloud seeding purposes. 

Dennis, Arnett S., South Dakota Numerical analysis of proposed hail Sept. 1, 1971 

School of Mines and Technology. suppression concepts. 
Firor, John W., National Center for National hail research experiment.. July 1, 1973 

Atmospheric Research. 

Fujita, Theodore T., University of Basic research on tornadoes relevant Sept. 1, 1971 

Chicago. to their modification. 
Fukuta, Norihiko, University of Development of cloud seeding gen- July 15, 1973 

Denver. erators for biodegradeable organic 

ice nuclei. 

Grant, Lewis 0., Colorado State Extended area effects from local Mar. 1, 1974 

University. weather modification. 

Cloud simulation and aerosol lab- Apr. 4, 1974 


Haas, J. Eugene, Human Ecology A comparative analysis of public re- Aug. 1, 1974 

Research Services, Inc. action to weather modification 


Hobbs, Peter V., University of Orographic snowfall in the Cascade Apr. 1, 1973 

Washington. project. 

Klein, Donald A. ( Colorado State Management of silver iodide used in July 1, 1974 

University. weather modification: Develop- 

ment in microbial threshold tox- 
icity criteria. 

Little, Gordon C, National Oceanic Operating two dual-Doppler radars June 1, 1974 

and Atmospheric Administration. in conjunction with the 1974 
summer operations. 

McQuigg, James D., University of Weather modification guidelines Feb. 15, 1974 


Moore, Charles B., New Mexico Lightning protection systems and May 15, 1974 

Institute of Mining and Tech- thunderstorm electrification, 

Mordy, Wendell A., Center for the A program of social science research Oct. 1, 1973 

Future. coordination and goal evaluation 

for Metromex. 

Ochs, Harry T., Ill, University of Supportive modeling of urban effects July 1, 1974.. 

Illinois. on precipitation. 
Plooster, Myron N., University of Microphysics — Diffusion interaction Apr. 15, 1974 

Denver. in ice nuclei plumes 
Schaefer, Vincent J., State University Second inadvertent weather modifi- April 1, 1974 

of New York cation workshop. 
Schickendanz, Paul T., Illinois State Climatic alterations in the Great June 1, 1974 

Water Survey. Plains due to widespread irriga- 


Simpson, Joanne, University of Evaluation and design of weather July 1, 1974 

Virginia. modification experiments. 
Steele, Roger L., University of Sequence effects of heterogeneous April 15, 1974 

Nevada nucleation. 
Taubenfeld, Howard J., Southern Study group on the societal conse- Oct. 1, 1973 

Methodist University. quences of weather modification. 

Veal, Donald L., University of Development of leaf-derived ice Apr. 1, 1973 

Wyoming. nuclei for weather modification. 
Warburton, Joseph A., University of Silver iodide seeding rates and snow- Mar. 1, 1973 

Nevada. pack augmentation. 


Inadvertent weather modification: 

Auer, August H., University of Modification of convective cloud activ- Apr. 1, 1975 

Wyoming. ity by an urban area. 

Braham, Roscoe R., Jr., Uni- Inadvertent weather modification in do 

versity of Chicago. the St. Louis area. 


t^s finn 

$JJ, ouu 


54, 000 

243, 000 


237, 500 


33, 500 


33, 500 


44, 400 


49, 800 




86, 300 


2, 000, 000 


55 400 


106, 900 


250, 000 


4, 000 


22, 800 


182, 000 


16 900 


in nnn 

1U, UUU 


42, 000 


1JU, uuu 




/ 0, UUU 


39, S00 


it nnn 
jj, UUU 


55, 500 


50, 000 




60, 800 


70, 000 


80, 100 






Table 14. Summary of Weather Modification Research Awards by NSF/RANN, for Fiscal Year 1973 through 1976 Transitional 
Quarter. (Data fiom Annual Summaries of Awards, RANN, Division of Advanced Environmental Research and Tech- 
nology.)— Continued 

Principal investigator/ Duration 

institution Title Effective date (months) Amount 

FISCAL YEAR 1975 AWARDS— Continued 
Inadvertent weather modification— Continued 

Chagnon, Stanley A., University Studies of urban effects on rainfall Apr. 1, 1975 12 $257,200 

of Illinois. and severe weather. 

Gossard, Earl E., National Dual-Doppler radar investigation of June 15, 1975 12 60,000 

Oceanic and Atmospheric Ad- wind flow patterns in Metromex. 


Ochs, Harry T., University of Numerical cloud modeling Apr. 1, 1975 10 63,400 


Schickedanz, Paul T., Univer- Climatic alternations in the Great June 1, 1974 24 55,500 

sity of lllinios. Plains due to widespread irriga- 

Societal utilization: 

Boone, Larry M., U.S. Depart- Economic and institutional consider- Oct. 1, 1973 15 54,500 

ment of Agriculture. ations of suppressing hail. 

Grant, Lewis O., Colorado State Extended area effects from local Dec. 1, 1974 12 280,000 

University. weather modification. 

Haas, J. Eugene Human Ecology A comparative analysis of public re- Oct. 1, 1974 12 76,000 

Research Service. action to weather modification 

Klein, Donald A., Colorado State Microbiological impacts of silver July 1, 1975 __ 12 46,600 

University. iodide used in weather modifica- 

McQuigg, James D., University Weather modification management Aug. 1, 1974. 14 41,000 

of Missouri. guidelines. 

Mordy, W. A., Center for the The importance of climate and July 1, 1974 15 87,000 

Future. weather alterations to mankind. 

Morgan, G. M., University of Design of a hail suppression experi- Nov. 1, 1974 12 67,800 

Illinois. ment in lllinios. 

Shaefer, Vincent J., State Uni- Second inadvertent weather modi- Apr. 1, 1974 12 33,000 

versity of New York. fication workshop. 

Taubenfeld, Howrad J., Southern Study group on the consequences of November 1974... 6 13,800 

Methodist University. weather modification. 
Weather hazard mitigation: 

Atlas, David, National Center National hail research experiment... July 1975 12 2,130,000 

for Atmospheric Research. 

•Moore, Charles B. t New Mexico Lightning protection and thunder- June 1, 1975 12 130,000 

Institute of Mining and Tech- storm electrification, 

Weather modification systems: 

Anderson, Charles E., Univer- Studies on the dynamics, micro- Jan. 1, 1975.. 12 96,000 

sity of Wisconsin. physics, and forecasting of severe 
local storms. 

Chisholm, John P., Sierra fJe- An accurate and inexpensive air- July 1, 1974 9 44,400 

vada Corp. borne windfinding system. 

Davis, Briant L., Institute of Chemical ccmplexing of silver iodide- Sept. 1, 1972 24 103,900 

Atmosphe ric Sciences. alkali iodide aerosols prepared for 
cloud-seeding purposes. 

Fukuta, Norihiko, University of Cloud-seeding generators for bio- July 15, 1974 12 100,400 

Denver. degradable organic ice nuclei. 

Grant, Lewis O., Colorado State Cloud simulation and aerosol lab- Nov. 1, 1974 12 18,000 

University. oratory. 

Little, Gordon C, National Oce- Dual-Doppler radar investigations of July 1, 1974 12 60,000 

anic and Atmospheric Ad- wind fields in severe storms. 


Simpson, Joanne, University of Evaluation and design of weather do 12 50,000 

Virginia. modification experiments. 


Improved weather modification 

Fukuta, Norihiko, University of Development of cloud-seeding gen- Aug. 1, 1975 12 133, 100 

Denver. erators for biodegradable organic 

ice nuclei. 

Gossard, Earl E., National Collection and processing of multiple May 15, 1976 14.5 135,000 

Oceanic and Atmospheric Doppler radar data in NHRE. 

Grant, Lewis O. Colorado State Testing and calibration program for July 1, 1975 12 10,800 

University. cloud-seeding materials, seeding 

generators, and nucleus-observ- 
ing instruments. 

Simpson, Joanne, University Evaluaion and design of weather do 9 73,000 

of Virginia. modification experiments. 

Silver iodide tracing in south Florida do 12 15,000 

Warburton, Joseph A., Denver Silver iodide seeding rates and do 6 49,900 

Research Institute. snowpack augmentation. 

Inadvertent weather modification: 

Auer, August H., University of Lidar, acoustic sounder and radi- July 15, 1975 12 52,800 

Wyoming. ometer investigation. 

Modification of convective cloud Feb. 1, 1976 14 178, 700 

activity by an urban area. 


Table 14. Summary of Weather Modification Research Awards by NSF/RANN, for Fiscal Year 1973 through 1976 Transitional 
Quarter. .(Data from Annual Summaries of Awards, RANN, Division of Advanced Environmental Research and Tech- 
nology.)— Continued 

Principal investigator/ 



Effective date (months) Amount 

FISCAL YEAR 1976 AWARDS-Continued ' 
Inadvertent weather modification— Continued 

Braham, Roscoe R., University Inadvertent weather modification in Feb. 1, 1976.. 

of Chicago. the St. Louis area. 
Changnon, Stanley A., Uni- Studies of urban effects on rainfall ...do_ 

versity of Illinois. and severe weather. 

Hobbs, Peter, University of Inadvertent weather modification by June 15, 1976. 

Washington. effluents from coal-fired electric 


Ochs, Harry T., University of Numerical cloud modeling: Applica- Feb. 1, 1976.. 
Illinois. tion to urban effects on precipita- 


Saxena, V. K., University of Airborne mapping of urban plume of May 15, 1976. 
Denver. St. Louis with a cloud condensa- 

tion nuclei (CCN) spectrometer. 

Social, legal, and economic impact of 
weather modification: 

Farhar, Barbara, Human Ecology A comparative analysis of public Dec. 1, 1975... 
Research Services, Inc. response to weather modification. 

Grant, Lewis 0., Colorado State A field experiment to test hypotheses 

University. of the reality, characteristic, and 

magnitude of extended area effects 
from weather modification. 
Klein, Donald A., Colorado State Management of nucleating agents Oct. 1, 1975... 
University. used in weather modification: De- 

velopment of microbial threshold 
toxicity criteria. 

Weather hazard mitigation: 

Veal, Donald, National Center National hal research experiment... Aug. 1, 1975.. 
for Atmospheric Research. 
Weather modification in support of 

Grant, Lewis 0., Colorado State An assessment of the present and July 1, 1975.. 
University. potential role in weather modifi- 

cation in agricultural production. 
Huff, Floyd A., University of Assessment of weather modifica- Nov. 1, 1975.. 
Illinois. tion in alleviating agricultural 

water shortages during droughts. 




15 82,000 
11 215,709 

12 2,361,000 

18 71,000 


I mproved weather modification tech- 

Chisholm, John, Sierra Nevada 

Hallett, John, University of 

Maki, Leroy R., University of 
Inadvertent weather modification: 
Uthe, Edward E., Stanford Re- 
search Inst. 

Social, legal, and economic impact 
of weather modification: 
Lambright, W. Henry, Syra- 
cuse Research Corp. 

Weather hazard mitigation: 

Auer, August H., University of 

Veal, Donald L., National Center 
for Atmospheric Research. 

An accurate and inexpensive air- Augus 

borne wind measuring system. 
An assessment of synoptic criteria 

for ice multiplication in convective 


Ice nucleation induced by bacteria.. 


Lidar and radiometric data analysis 
of mixing levels, clouds, and 
precipitation processes. 

The utilization of weather modifica- September 1976. 
tion technology: A State govern- 
ment decisionmaking study. 

The kinematics of thunderstorm August 1976 

gust fronts relating to the mitiga- 
tion of airport flight hazards. 

National hail research experiment... July 1976 




18 60, 400 

12 56, 300 

Weather hazard mitigation 

Research supported by NSF in this category is pointed toward the 
reduction of undesirable aspects of selected weather hazards. Although 
the major effort has been in research on the reduction of hail damage, 
research related to other severe weather phenomena lias included in- 
vestigations on lightning protection, wind shear warning, and fog 
hazard alleviation. The major project in weather hazard mitigation 


in recent years has been the National Hail Research Experiment 
(NHRE), which was initiated by the Foundation in 1971 "to assess 
the potential for altering hail ... by cloud seeding' and determine the 
extent to which beneficial modification can be accomplished effectively 
on an operational basis." 42 

The concept of a national hail suppression experiment grew out of 
interest by U.S. scientists in hail suppression activities in the Soviet 
Union in the 1960's and also from the 1965 recommendation of the 
Interdepartmental Committee for Atmospheric Sciences (ICAS) that 
the Foundation, in collaboration with other Federal agencies, should 
develop a plan for hail suppression research. 43 As a first step in plan- 
ning such a national effort, the NSF invited the National Center for 
Atmospheric Research (NCAR) to cooperate in organizing the First 
National Symposium on Hail Suppression, which was held at Dillon, 
Colo., on October 14-15, 1965, under the chairmanship of Verner E. 
Suomi. 44 

Arising from the Dillon conference was an NSF-sponsored Hail Sup- 
pression Research Steering Committee, also chaired by Dr. Suomi, 
which held a number of meetings in the years immediately following 
and prepared a hail suppression test outline in 1968. 45 Upon approval 
of the outline by the ICAS, the NSF requested that a detailed plan 
for a national experiment be developed by NCAR. A "Plan for the 
Northeast Colorado Hail Experiment (NECHE)" was prepared by 
NCAR 46 and approved by the ICAS in 1969. The NECHE plan called 
for an intensive investigation into hailstorms and hail suppression to 
be conducted over a 5-year period. After a few years of preliminary 
investigations, the project was eventually renamed the National Hail 
Research Experiment (NHRE) in 1971. 

NHRE was one of seven proposed national projects in weather 
modification identified by the Interdepartmental Committee for At- 
mospheric Sciences (ICAS) in 1971. 47 The National Science Founda- 
tion, which originally planned the experiment, was recommended as 
the lead agency for the project, and assistance was to be offered by the 
Departments of Agriculture, Commerce, Defense, Interior, and Trans- 
portation and by the Atomic Energy Commission and the National 
Aeronautics and Space Administration. 48 

Although there was interagency cooperation in planning the experi- 
ment and some support to the project during early years by some of 
the aforementioned agencies, eventually, most of the other agencies 
pulled out and NSF had to provide full support on its own. In a 1974 
investigation of the Federal weather modification program, the Gen- 
eral Accounting Office (GAO) concluded that "even though the ex- 

42 Downie and Dirks, "National Science Foundation Weather Modification Program," 
1976. p. 557. 

43 National Science Foundation. "Renort of the First National Symposium on Hail Sup- 
pression." Dillon, Colo., Oct. 14-15, 1965, p. 1. 

44 Ibid. 

43 National Science Foundation. Hail Suppression Research Steering Committee, "Outline 
of a Hail Suppression Test." March 1968, p. 1. 

48 National Center for Atmospheric Research and Select Planning Group of the Northeast 
Colorado Hail Experiment, "Flan for the Northeast Colorado Hail Experiment," Boulder, 
Colo.. Mar. 17. 1969. 

47 Federal Council for Science and Technology. Interdepartmental Committee for Atmos- 
pheric Sciences. "A National Program for Accelerating Progress in Weather Modification," 
ICAS rept. No. 15a, June 1971, p. 21. (The seven national projects are listed in this report, 
p. 225. ) 

48 Ibid., pp. 35-37. 


periment was well planned, requiring extensive interagency participa- 
tion, * * * for the most part, agencies could not and did not meet all 
their obligations." 49 The GAO study observed that, because of the 
withdrawal of some of the intended support, "important segments of 
research were lost for 1973" and that each operational season would 
continue to have problems with commitments from participating 
agencies. 50 The other national projects recommended by the ICAS, 
each with much less coordinated planning than XHRE or with no such 
coordinated planning at all, failed to materialize as truly national 
projects, although some were pursued as major single-agency projects. 

NHRE was based on the original NECHE plan prepared for the 
XSF by the Xational Center for Atmospheric Research (NCAR) , and 
management for conduct of the experiment was assigned to NCAR 
by NSF. The experiment was a cooperative effort between NCAR and 
10 universities, funded by NSF, with additional support from the De- 
partment of Commerce (National Oceanic and Atmospheric Admin- 
istration), the Department of Transportation (Federal Aviation Ad- 
ministration), and the Department of Defense. Figure 9 is a map of 
the northeastern corner of Colorado, showing the two areas between 
Sterling, Colo., and Kimball, Nebr., which were target areas for the 
NHRE. Field headquarters for the experiment were located near 
Grover, Colo. Figure 10 is a more detailed NHRE map, showing the 
special use airspace and the protected area as well as the mesonet and 
rawinsonde site locations during the 1974 season. 




K J05 km GROVER 



f / 





/\! ( 

/\ > FT COLLINS [ - 

\ ' O " ' 










I I I I 

Figure 9. — Location map, showing the vicinity of northeastern Colorado where 
the National Hail Research Experiment (NHRE) was conducted. NHRE field 
headquarters were located near Grover, Colo. The two areas outlined between 
Sterling and Kimball were the target areas for the seeding program in 1072 
southern area) and in 1973 and 1974 (northern area). (From Wade, et al.. 
1977. ) 

49 Comptroller General of the United States. "Need for a National Weather Modification 
Research Program," report to the Congress, U.S. General Accounting Office, B-133202, 
Auk. 23. 1074. pp. 10-22. 

60 Ibid., p. 20. 



pecial Use Air 



■ «lil»iiiimn ii 



mov^.e n 


\ SiDN£y\ r— i lODOEPOlE B 

^ AREa 

\^»r» ® E 




» ,j 

« V 


'k • 

t riiu ! 


E -o 


d o«p*.'" * 



J* °" ~ 

1 ^ 



<r / 



— fi 


° h= T ,W. M.ES 

s — * ,M » y ■ * r ... 

Figure 10. — Detailed location map for the National Hail Research Experiment 
(XHRE), showing the special use airspace and protected area, as well as the 
mesonet and rawinsonde site locations during the 1974 summer season. (Cour- 
tesy of the National Science Foundation.) 

Following collaborative studies of northeast Colorado hailstorms 
by NCAR, Colorado State University, and the U.S. Department of 
Commerce during the period 1968-70, what was to become the National 
Hail Research Experiment (XHRE) effectively began in the summer 
season of 1970 with the following twofold plan : 

1. To carry out research into those processes important to the under- 
standing of hail production in severe thunderstorms, and 

2. To perform a randomized test of a hail suppression technique 
modelled in some important respects after the reportedly successful 
operation in the Soviet Union. 

The twofold objective of XHRE has remained throughout the proj- 
ect : however, its statement has varied from year to year in response to 
changes in emphasis both at XSF and at NCAR. In particular, after 
transfer of the project to RAXX. an important emphasis was given 
to social, economic, legal, and environmental studies in connection with 
the potential impact of hail suppression. 

A preliminary field program, for instrument testing and field experi- 
ence, was undertaken during the summer of 1971 ; and during the 
summers of 1972, 1973, and 1974 the major randomized hail sup- 
pression test was conducted along with other basic research on hail 


properties. Instead of continuing the randomized seeding experiment 
for the planned 5 years, it was curtailed at the close of the 1974 season 
because research evidence showed strongly that seeding as performed 
was not likely to suppress hail in northeast Colorado and preliminary 
analysis indicated that data from 2 more years was unlikely to demon- 
strate a suppression effect. 51 At a symposium on hail and hail suppres- 
sion in the fall of 1975, 52 most of the experts agreed that continuation 
of the 1972-74 randomized seeding experiment was unwise for the 
reasons given above. 

A revised plan for NHRE followed this symposium, in which it 
was stated that future research should be directed "* * * to combine 
applied research, development of techniques, and redesign of a ran- 
domized seeding experiment in a manner which will provide the great- 
est chance of reaching a conclusive answer as to the feasibility of hail 
suppression in a reasonable time." 53 The revised plan also committed 
the NHRE staff to completion of a report on the 1972-74 randomized 
seeding experiment. The five-volume report, the first volume of which 
is a summary of the analysis and results, has recently been completed 
and distributed. 54 

A short field season for NHRE was undertaken during 1975 to test 
new instruments and a new data system aboard the South Dakota 
School of Mines and Technology armored, penetrating T-28 aircraft. 
Operated in coordination with the Grover S-band radar, the Grover 
control center, and the aircraft tracking system, the test was successful 
and valuable data were obtained. Field measurements were carried out 
on a larger, more comprehensive scale during the summer of 1976 ; how- 
ever, no seeding was done. 55 Analyses of data from previous years con- 
tinued in 1976 and 1977. Field research in 1976 and succeeding analyses 
were intended to assist in an improved design for a randomized seeding 

Highlights of the results obtained by intensive analysis of the data 
obtained from NHRE through the 1975 summer field season have been 
summarized by Downie and Dirks as follows : 56 

1. The original techniques employed in NHRE were based on con- 
cepts developed in the Soviet Union, which hypothesized that rapid 
hail growth took place in local regions of liquid water accumulation 
zones. A variety of observations has led to the rejection of the Soviet 
model of hail formulation for northeast Colorado storms. 

2. Observations within the clouds and examination of thin sections 
of hailstones indicate that the iee-cryst a 1 -riming (graupel) process is 
dominant rather than the waterdrop-coalescence mode of precipitation 

D1 Ibid., pp. 3-4. 

G2 National Center for Atmospheric Research. "NHRE Symposium/Workshop on Hail and 
Its Suppression," Estes Park, Colo., Sept. 21-28, 1975. National Hail Research Experiment 
technical report NCAR/7100 75/2. Boulder, Colo., November 1975 130 pp. 

53 National Hail Research Experiment Staff, revised plan for the National Hail Research 
Experiment. National Center for Atmospheric Research, Boulder, Colo., February 1976, p. 3. 

"Crow. B. L., P. W. Summers A. B, Long, C. A. Knight, G. B. Foote, and J. E Dye. final 
report — "National Hall Research Experiment : Randomized Seeding Experiment: 1972-74. 
Vol. I. I<]xperimental Results and Overall Summary. " National Center for Atmospheric Re- 
search. Boulder, Colo., December 1976. 260 pp. [Vols. II, III, IV, and V deal with precipita- 
tion measurements, meteorological summary, radar summary, and hail declaration proce- 
dures ;ind seeding operations, respectively.] 

"University Corp. for Atmospheric Recearch. "Fiscal Year 1978 Work Plan for Analysis 

of Data From the National Hail Research Experiment,** p. 3. 

^Downie and Dirks, "National Science Foundation Weather Modification Program," 
1976, pp. 557-558. 


3. Much effort was expended in the development of new instru- 
mentation during the NHRE experiment to provide direct measure- 
ments of the characteristics of hail-producing storms which were 
necessary to validate the concepts of hail suppression. 

4. Eesults from the randomized seeding experiment, which was car- 
ried out during the period 1972-74, do not permit one to conclude that 
seeding had any effect on hail or rainfall. However, the data are ex- 
tremely valuable for determining the required density and extent of 
surface instruments for a future seeding experiment, as well as esti- 
mating the length of time a future experiment would have to be carried 
out to detect a specified effect. 

5. Studies of direct economic costs and benefits have provided esti- 
mates of the breakeven point for operational cloud seeding and reiter- 
ated the value of hail suppression if reductions in damage of at least 10 
percent are attainable. 

Referring to the randomized seeding experiment, conducted from 
1072 through 1974, the following conclusion was made in the final 
report : At the outset, the total mass of hail at the ground in the target 
area was identified as the primary response variable for evaluating 
seeding effects on hailfall. The major conclusion of the experiment is 
that no statistically significant effect of seeding is detected. This result 
is true for the hail mass and all other response variables considered, 
regardless of the method of analyzing the data. 57 

In a recent paper by Knight, Foote, and Summers it was concluded 
that "at the present state of knowledge of hail formation in storms, it 
would appear to be premature to start another major statistical seeding 
experiment. There is no new, very promising technique in the offing, as 
the Soviet method appeared to be when NHRE started." 58 The authors 
further state that scientific research necessary for a solid foundation 
for new attempts to modify the precipitation from convective storms is 
underway and provide the following summary of positive results from 
N HRE : 

The National Hail Research Experiment included a first attempt at mounting 
a hail suppression test with a strict randomized design and evaluation based 
upon physical measurement of hail rather than crop damage. The results have 
l»een analyzed in detail, with extensive evaluation of data quality and of opera- 
tional success, facets not generally treated in such detail in previous programs. 
Tlie outcome was that the seeding may have had a variety of non-zero effects or 
no effects at all. The one conclusive result was to rule out very large increases or 
decreases of hail or rain by the seeding. The physical research portion of NHRE 
led to advances in knowledge of hail and of storms, and contributed substantially 
to the development of the research tools . . . needed to derive answers to the 
oul standing, practical problems. 50 

Figure 11 shows the components of the Portable Automated Mesonet 
(PAM) data network. There were 15 of the remote PAM stations in 
the. XHRE observing network during the 1976 field season. Each 
PAM station measures pressure, temperature, moisture, precipitation, 
and wind direction and speed. Data are telemetered to a central collec- 
tion point, in real time if needed, or they are stored at the PAM 
station and collected at the central collection point daily. 

fi ' Crow, et al.. "Final Report — National Hail Research Experiment : Randomized Seeding 
Experiment : 1972-74." vol. 1. 1976. p. iii. 

Knight. Charles A.. G Brant Foote, and Peter W. Summers, "Physical Research and 
General Conclusions from the National Hail Research Experiment." preprints from the 
"Sixth Conference on Planned and Inadvertent Weather Modification." Champaign-Urbana, 
111.. Oct. 10-13, 1977. American Meteorological Society, Boston, Mass., p. 165. 

59 Ibid. 




Figure 11. — Components of the Portable Automated Mesonet (PAM) data col- 
lection system, used in the National Hail Research Experiment (NHRE). Each 
PAM station measures pressure, temperature, moisture, and wind speed and 
direction; data are then telemetered to a central collection point. (Courtesy 
of the National Science Foundation.) 

A typical remote field installation of the portable automated mesonet (PAM) 
system. (Courtesy of the National Science Foundation.) 


Weather modification technology development 

Research sponsored by the NSF under this category is intended 
to utilize predictive models, advanced measurement systems, and 
statistical analyses to improve the experimental design and evaluation 
of weather modification investigations. Part of the demand for some 
of the long, costly weather modification experiments is due to the 
large natural variability of atmospheric processes, which is a major 
obstacle to successful field tests of weather modification technology. 
It is expected that improvements achieved through the high priority 
research incorporating the combined use of the three research tools 
listed above will not only aid in the logistic design of experiments, 
but will also reduce the predicted natural variability of weather 
events, thus reducing the overall time required for conducting a de- 
finitive experiment. 60 

The NSF-supported Climax experiments (conducted by Colorado 
State University from 1960 to 1970) first demonstrated the efficacy 
of wintertime orographic precipitation enhancement. Results of these 
experiments have provided the basis for a number of subsequent dem- 
onstration experiments. 61 The following examples of weather modifi- 
cation technology development projects have received NSF research 
support in recent years : 62 

1. Evaluation of the Florida area cumulus experiment (FACE), 
where cloud motion has been found to be a significant covariate in the 
data evaluation. 

2. Development of new techniques for the evaluation of convective 
precipitation in the metropolitan meteorological experiment (Metro- 

3. Development and testing of statistical- physical methods for the 
evaluation of operational cloud-seeding programs. 

4. Research on various ice nucleants which might be used instead of 
silver iodide and on development of delivery systems for organic 

5. Assessment of Midwest cloud characteristics for weather modifi- 
cation, by compiling and analyzing sample statistics of variables im- 
portant in cloud development and precipitation processes as well as in 
their modification as a function of mesoscale and macroscale atmos- 
peric conditions. 

6. Exploration of the feasibility of artificially generating cirrus 
clouds as a weather modification tool and numerical modeling of ef- 
fects of cirrus clouds on the troposphere and mesoscale weather. 

7. Maintenance and operation of a testing and calibration facility for 
seeding materials, cloud-seeding generators, and ice nucleus measur- 
ing instrumentation, for use by research projects of Federal agencies 
and by the commercial cloud-seeding industry (at Colorado State 

Other specific research projects designed to improve the technology 
of weather modification are found in the list of recent RANN awards 
for weather modification research in table 14. In the past, the NSF 
program in weather modification has made significant contributions to 

80 Federal Council for Science and Technology, Interdepartmental Committee for Atmos- 
pheric Sciences, ICAS 20-FY77, p. 96. 

81 The Climax experiments are discussed under orographic precipitation enhancement tech- 
nology, in ch. p. 77. 

62 Downie and Dirks, "National Science Foundation Weather Modification Program," 1976. 
p. 560 ; and Currie S. Downie, personal communication. 


the initial phases of major weather modification projects of other Fed- 
eral agencies, such as Project Stormfury (Department of Commerce) 
and Project Skyfire (Department of Agriculture) . 

Instrumented aircraft, operated by the Research Aviation Facility of the National 
Center for Atmospheric Research (NCAR), whose primary mission in the 1976 
summer field season of the National Hail Research Experiment (NHRE), was 
to assess the feasibility of on-top cloud seeding. (Courtesy of the National 
Science Foundation.) 

Inadvertent weather modification 

The objective of this portion of the NSF/RANN weather modifica- 
tion research program is "to delineate the mechanisms whereby, and 
the extent to which, an agricultural region modifies its own climate 
and an urban area modifies its surrounding weather, precipitation, and 
aerosol." 63 Most of the NSF research on inadvertent weather modifi- 
cation is concentrated in the metropolitan meteorological experiment 
(METROMEX) in the neighborhood of St. Louis. The research seeks 
to provide better definition of the causes for anomalies in precipitation 
and other atmospheric properties observed as a result of the urban in- 
fluence. In addition to METROMEX other inadvertent weather modi- 
fication research in which NSF has interest includes studies on the ef- 
fees of energy development, expanded agricultural production, and 
growing urban sprawl. 64 

One current NSF-sponsored project is being conducted by the Uni- 
versity of Washington on inadvertent effects induced by coal-fired 
electric powerplants. The objective of this research is to determine 

63 National Science Foundation, "Summary of Awards : 1976," Division of Advanced En- 
vironmental Research and Technology, Washington, D.C. (no publication date), NSF-RA- 
760219, p. 97. 

64 Federal Council on Science and Technology, Interdepartmental Committee on Atmos- 
pheric Sciences, ICAS 20-FY77, pp. 96-97. 


the effects on visibility, clouds, and precipitation of the effluents from 
modern coal powerplants. Such effects may be considerable since the 
plants emit much heat, moisture, particulates, and gaseous material 
into the atmosphere. Results from the project are expected to aid in 
evaluation of environmental effects of these generators and to assist in 
the siting of new powerplants. Principal users of the results include 
regional, State, and Federal agencies concerned with energy develop- 
ment, research, ecology, and land development, as well as engineering 
firms involved with air pollution impact studies and control systems. 65 

The subject of another inadvertent weather modification study is 
the influence on the climates of the Great Plains by widespread irriga- 
tion. The main objective of this research is to determine the effects on 
precipitation; also of concern are influences on other meteorological 
parameters. Results show the existence of rainfall anomalies over an 
area comparable in size to the irrigated area, and the effects are most 
detectable during wet summer months. 66 

METROMEX is a multi-institutional, multiyear research project 
sponsored by the NSF and several other Government agencies, at- 
tempting to discover causes for, and to assess consequences of, urban- 
ind'uced eather effects at St. Louis and vicinity. Primary goals of 
METROMEX are the systematic investigation of : 67 

The effects of a large urban complex on the frequency, amount, 
intensity, and duration of clouds, precipitation, and related severe 
weather; and 

The conditions whereby the urban complex modifies the precip- 
itation process. 

Application related goals of the experiment are investigation and 
activities : 68 

To study and develop techniques for translating the results of 
the scientific goals to other urban areas so as to predict the urban- 
related changes in other cities ; 

To translate relevant results to a wide variety of users in the 
scientific, government, and business communities ; 

To provide the basis for studies of the potential changes in cli- 
mate relating to megalopolis and to major land use changes. 
A wide variety of potential users of the information from METRO- 
MEX include urban and regional planners, meteorologists, hydrol- 
ogists, airport planners and operators, and air quality scientists. The 
study is relevant to impacts of increased use of coal, large concentra- 
tions of electrical energy generators in power parks, and long range 
consequences of air pollution on climate. 69 

METROMEX is the world's first major field program planned to 
link urban land use with modification of the surrounding weather. The 
selection of St. Louis as the site for the experiments was based on the 
relatively simple topography of the city and its surroundings, the 
existence of farmlands downwind to the east in the "shadow" of the 

85 National Science Foundation. Division of Advanced Environmental Research and Tech- 
nology, "Summary of Awards : 1976," p. 99. 

w Downie and Dirks, "National Science Foundation Weather Modification Program," 1976. 
p. 559 . 

m "Principal Investigators of Project Metromex. Metromex Update." Bulletin of the 
American Meteorological Society, vol. 57, No. 3, Mar. 1976, p. 304. 
" Ibid. 

» Downie and Dirks, "National Science Foundation Weather Modification Program," 1976. 
p. 559. 


city on which urban influences can be studied, the relatively unclut- 
tered airspace above the city which permitted research flights and 
atmospheric experiments, and the patterns of urbanization which are 
typical of other areas in midlatitude North America. 70 

Most of the METROMEX field activities were conducted during the 
summer months in a 2,000-square-mile area about 56 miles in diameter 
which includes St. Louis and the Alton-Wood River industrialized area 
to the northeast. A larger 3,800-square-mile area which includes St. 
Louis and extends downward contained the world's largest rain-gage 
network. 71 These two areas are shown in figure 12. 


Figure 12. — METROMEX field experiment area, centered in St. Louis, and ex- 
tended "downwind" area containing network of rain gages and other instru- 
mentation. (From Changnon ad Simonin. Studies of selected precipitation 
cases from METROMEX. Illinois State Water Survey, Urbana, 1975.) 

70 National Science Foundation, "Do Cities Change the Weather?" Mosaic, vol. 5, No. 3, 
summer 1974, p. 30. 
1 1bid. 

34-857 O - 79 - 21 


Within the research and data collection areas, measurements have 
been made of the speeds and direction of winds at different heights and 
locations, of temperatures, cloud dynamics, precipitation, the nature 
and intensity of pollutants, number and sizes of storms, and the quality 
and quantity of ground water under different weather conditions. 72 

Planning for METKOMEX was initiated in 1969-70 by scientists 
from the Illinois State Water Survey, the University of Chicago, the 
University of Wyoming, and Argonne National Laboratory. The ex- 
perimental field program was launched in 1971, supported in part by 
the Atomic Energy Commission, the Department of Health, Educa- 
tion, and Welfare, and the State of Illinois, as well as the National Sci- 
ence Foundation. Other research groups which later participated in the 
project include Stanford Research Institute, Battelle Pacific North- 
west Laboratories, the University of Missouri, Sierra Nevada Corp., 
and the University of California at San Diego. 73 Field measurements 
in METROMEX were essentially completed during 1976; although 
the final METROMEX project report is expected to be published in 
the near future, the analysis of the large amount of collected data 
should continue for some years. 

In a 1976 review of project accomplishments, the following findings 
from METROMEX were summarized : 74 

1. There is a summer precipitation anomaly at St. Louis, varying 
between a 10 and 30 percent excess above background, the location 
and intensity of which vary with the prevailing seasonal storm motions 
and general character of summer weather. 

2. Some individual rain intensity centers of showers or thunder- 
storms that develop or pass over St. Louis and over the Alton-Wood 
River industrial area appear to be enhanced significantly (94 and 73 
percent, respectively) . 

3. The major precipitation changes in and east of the urban indus- 
trial area seem to occur during squall line or squall zone conditions 
when nature is capable of producing moderate to heavy rains, result- 
ing in a 60 percent or greater increase in heavy rain (greater than or 
equal to 3 cm.) days, a 25 percent increase in thunderstorm activity, 
and an 80 percent increase in hailstorms and hail intensities in and 
just east of the city. Radar shows a region of maximum development 
of large thunderstorms extending to 100 kilometers northeast from 
the city. 

4. Like most large cities, St. Louis has a marked heat island and an 
identifiable minimum in specific humidity. These effects are most 
marked at the surface, but often show height-averaged temperature 
excesses of 1 degree K and moisture deficits of 1 gram of water vapor 
per kilogram of air, relative to nearby rural areas, extending through 
the mixing layer to cloud bases. 

5. The low-level air flow under light wind conditions is markedly 
perturbed by the city and often results in distinct convergence over 
and just downwind of the city center. 

6. The pattern of production of Aitken condensation nuclei (ACN) 
and cloud condensation nuclei (CCN) has been developed for the 
area. Elemental emission rates have been measured. 

" Ibid. 

73 Principal investigators of Project Metromex. Metromex update, 1976, p. 304. 
71 Ibid., pp. 304-305. 


7. Convective storms in the St. Louis area are significant mechanisms 
for removal and deposition of urban pollutants. 

Mechanisms which, in varying degrees, may be responsible for ob- 
served downwind increases in summer precipitation, heavy rain occur- 
rences, and hail activity include the large quantities of particulate 
and gaseous matter injected by industries and motor vehicles into the 
atmosphere, the heat added and heat island effects of the urban area, 
the anomalous moisture patterns over the city, and the increased 
turbulence and wind perturbation caused by the roughness of the 
city's surface and the heat island. 75 It has further been observed that 
the 10 to 30 percent increase in summer rainfall over the 2,000-square- 
mile area east of St. Louis produces a 15-percent average increase in 
streamflow and increased infiltration of ground water. 76 

Societal utilization activities 

The purposes of this portion of the NSF/RANN" program, con- 
cerned with social, legal, environmental, and economic impacts of 
weather modification, are "to evaluate societal reaction to weather 
modification, to determine societal expectations, and to identify the 
needs for the scientific base necessary to bring about successful appli- 
cation of weather modification." This research "extends across the 
disciplines of political, social, legal, economic, ecological, and physi- 
cal sciences in an effort to investigate the impact of weather modifi- 
cation technology on man." 77 A number of studies have been sup- 
ported by the Foundation in this category, in which these aspects of 
weather modification are examined. 

A study group on the societal consequences of weather modification 
was formed in 1973 at the request of the Interdepartmental Commit- 
tee for Atmospheric Sciences (ICAS). This study, sponsored by the 
NSF, was designed to examine needs of the Nation for a weather modi- 
fication capability and to determine if the present Federal weather 
modification program is directed toward meeting those needs. Results 
of this investigation, now nearing completion, should be useful in 
identifying the alterations or redirections of the Federal program 
required to meet societal goals. 78 

Studies in social, legal, economic, and ecological aspects of weather 
modification that are currently underway or have recently been com- 
pleted include the following : 

1. Preparation of a compendium on economic impacts of weather 
variability, by the University of Missouri. This report was designed 
to present quantified relations between weather and certain basic 
human activities, such as agriculture and energy use. 79 

2. A comparative analysis of public response to weather modifica- 
tion, by Human Ecology Research Services, Inc. Building on results 
of 6 years of sociological study of public response to weather modifi- 
cation, this research will examine social response to weather modifica- 
tion in South Dakota and test preliminary hypotheses on acceptance 
and rejection processes. Validation of the preliminary hypotheses and 

75 Downie and Dirks, "National Science Foundation Weather Modification Program," 
1976. p 559. 
7 « Ibid. 

77 National Science Foundation. Division of Advanced Environmental Research and Tech- 
nology, "Summary of Awards : 1976," p. 101. 

78 Downie and Dirks, "National Science Foundation Weather Modification Program," 1976, 
p. 560. 

79 Ibid. 


response, patterns will provide the framework for development of a 
causal model of the acceptance/rejection process. 80 

3. Field experiment to test a hypothesis of the reality, characteris- 
tic, and magnitude of extended area effects from weather modification, 
by Colorado State University. With increasing evidence that planned 
weather modification projects may have effects that extend over broad 
geographic areas, this research is an investigation of "downwind'' 
effects of past experiments in the Rocky Mountains and the Great 
Plains of the United States and in Israel, extending an earlier 3-year 
study of such effects. Physical and statistical analyses are combined 
to determine such extended area effects and to develop hypotheses de- 
scribing processes which produce the effects. The project also includes 
design of a field experiment based on results of these post hoc analyses 
and on current results from modeling studies and physical experi- 
ments. This research is intended to provide a basis for evaluating 
extended-area effects on societal activities and should be valuable in 
formulation of policies on public issues in weather modification. 81 

4. Management of nucleating agents used in weather modification 
and development of microbial threshold toxicity criteria, by Colorado 
State University. The purpose of this research is to provide informa- 
tion on possible long-term effects of weather modification nucleating 
agents on microbial ecosystems, concentrating on soil and aquatic eco- 
systems, which are the most critical areas for accumulation of the 
agents. Results of this study will be used to prepare environmental 
impact statements for silver iodide seeding in various experimental 
and operational cloud seeding programs. 82 In the final phase of this 
study, a workshop on the environmental impacts of cloud seeding 
materials was conducted in Vail, Colo., in November 1976. The pro- 
ceedings of the workshop are expected to be published during 1978. 

5. Utilization of weather modification technology : A State govern- 
ment decisionmaking study, by Syracuse University. State govern- 
ments have taken the lead in developing regulatory policies affecting 
the present use of weather modification technology: however, such 
policies cover a wide spectrum, some being highly restrictive while 
others are more permissive. This study, focusing on decisionmaking 
processes in five States — South Dakota. Colorado, Illinois, Pennsyl- 
vania, and California — will develop case histories and analyses of 
policymaking, the availability of which should help Federal and State 
officials in making decisions on emerging weather modification 
technology. 83 

Agricultural iceather modification 

This relatively new portion of the NSF/RANN weather modifica- 
tion program is* evolving in response to a need "to develop a better 
understanding of weather variability and its significance to food pro- 
duction and to develop specific applications of weather modification 
technology as it relates to agricultural needs. 84 For such applications, 
weather modification is considered in a broad context, including all 
identifiable modifications of the atmospheric environment. 

» National Science Foundation. Division of Advanced Environmental Research and Tech- 
nologv, "Summary of Awards : 1976," p. 101. 
81 Ibid., p. 102. 

w National Science Foundation. Division of Advanced Environmental Research and Tech- 
nology. "Summary of Awards: Transition Quarter 1976." NSF 77-8. Washington, D.C. 
(no publication date) , j). 48. _ . , _ . . ,-__«, 

«• National Science Foundation. Division of Advanced Environmental Research and Tech- 
nology, "Summary of Awards : 1976," p. 105. 


A major study, which included an assessment of the potential of 
weather modification in support of agriculture, was recently com- 
pleted by the National Academy of Sciences (NAS) /National Re- 
search Council. The investigation dealt with changing weather and 
climate patterns and their effects on agricultural and renewable re- 
sources productivity. 85 These implications were examined by the com- 
mittee in climate and weather fluctuations and agricultural produc- 
tion, which was established by the NAS in June of 1975 at the request 
and with the support of the National Science Foundation. Among 
other considerations, a chapter of the committee's report was devoted 
to weather modification, covering such topics as the feasibility of 
weather modification, crop-weather relationship and weather modifi- 
cation, impact variability, and societal and environmental issues. The 
committee made the following recommendations : 86 

Intensive efforts should be made to apply existing basic knowl- 
edge of atmospheric and cloud processes in specific applied re- 
search programs to benefit agriculture. Methods of applying the 
benefits of demonstrated or nearly demonstrated weather modi- 
fication techniques to specific crop needs, incorporating water 
storage, and other water management procedures, should be devel- 
oped. Proper recognition of societal concerns must be included. 

Gaps in basic knowledge of agriculturally oriented weather 
modification should be identified, and research initiated to fill 
them. Results of this research should be applied on an interactive 
basis with ongoing research and application projects. Important 
segments of the basic research should address the exploration of 
new ideas and approaches. 

Government organizational structures and policies should in- 
sure an integrated approach to weather modification research so 
that related problems such as rain and hail from convective sys- 
tems can be treated in the same experimental framework. Research 
programs should be interdisciplinary, should draw on the expertise 
available from Government agencies and from the academic and 
private sectors, and should incorporate a productive mix of big 
science — permitting large, pooled facilities — and small science — 
encouraging small group initiatives. The growing collaboration 
between scientifically and operationally oriented weather modi- 
fication experts should be focused on key crops and agricultural 

Two other recent NSF-sponsored research projects on weather modi- 
fication in support of agriculture are: 

1. An assessment of the present and potential role of weather modi- 
fication in agricultural production, conducted by Colorado State Uni- 
versity. This research was intended to identify potential capabilities of 
weather modification in terms of agricultural productivity and to 
focus priorites for weather modification research in terms of maximum 
benefits to agriculture. The research plan included a workshop of ex- 
perts in agriculture and weather modification in order to develop an 
authoritative document on the role of weather modification in increas- 
ing world agricultural production. 87 

83 National Academy of Sciences, National Research Council, "Climate and Food ; Climate 
Fluctuation and U.S. Agricultural Production." a report of the Committee on Climate and 
Weather Fluctuations and Agricultural Production, ISBN 0-309-02522-2, Washington, 
D.C., 1976. 212 pp. 

86 Ibid., p. 131. 

87 National Science Foundation. Division of Advanced Environmental Research and Tech- 
nology, "Summary of Awards : 1976," p. 105. 


2. Assessment of weather modification in alleviating agricultural 
water shortages during drought, conducted by the Illinois State water 
survey. The purpose of this study was to provide information needed 
in decisionmaking processes regarding use of weather modification for 
mitigation of agricultural droughts in the Midwest and other similar 
areas. This research was intended to contribute to man's knowledge of 
the limitaitons of weather modification to planned precipitation aug- 
mentation for agricultural applications and to assist in determining the 
scope and duration of future weather modification research in similar 
climatic regions of the world. 88 


Introduction and general discussion 

Within the Department of Commerce the research program in 
weather modification is conducted by the Environmental Research 
Laboratories of the National Oceanic and Atmospheric Administration 
(NOAA). Through NOAA's predecessor organizations, the U.S. 
Weather Bureau and the Environmental Science Services Administra- 
tion (ESSA), the Commerce Department has been active in weather 
modification since 1946, with research programs directed at modifying 
severe storms such as hurricanes, increasing rainfall from tropical 
cloud systems, and suppressing lightning in thunderstorms. The two 
major ongoing research projects are the Florida Area Cumulus Ex- 
periment (FACE) , a project to demonstrate the possibility of increas- 
ing precipitation from convective cloud systems through dynamic seed- 
ing, and Project Stormfury, intended to mitigate the severe impacts of 

The NOAA Research Facilities Center (RFC) , is an operational and 
technical organization, with the mission of providing instrumented air- 
craft for research programs of NOAA and other Government agencies, 
including weather modification projects. Part of NOAA's overall 
weather modification effort is its program of Global Monitoring for 
Climatic Change (GMCC), under which measurements are made of 
natural and manmade atmospheric trace constituents in order to deter- 
mine their increases or decreases and possible influences on climatic 
change. Other research in recent years has been concerned with modi- 
fication of extratropical severe storms and in suppression of lightning, 
the latter in cooperation with the National Aeronautics and Space Ad- 
ministration (NASA) in connection with protection of launch vehicles. 

In addition to these activities intended to explore weather modifica- 
tion and develop techniques for controlling the weather, NOAA also 
conducts background research in a variety of areas of atmospheric sci- 
ence that is essential to the future of weather modification development. 
Included are modeling and theoretical work on the structure, dynamics, 
and energy processes of severe storms such as hurricanes, tornadoes, 
and thunderstorms. Also pertinent is the development of instrumenta- 
tion for direct measurement of atmospheric properties and for remote 
probing of the atmosphere. 89 

A summary of the funding for the NOAA weather modification 
program for fiscal year 1976 through fiscal year 1978 (estimated) is 
contained in table 15. 

88 Ibid., pp. 105-106. 

w Townsend, John W., testimony In : U.S. Congress. House of Representatives, Committee 
on Science and Technology. Subcommittee on the Environment and the Atmosphere, "Weath- 
er Modification," hearings. 94th Congress, 2d session, June 15-18, 1977, Washington, D.C, 
U.S. Government Printing Office, 1976, p. 171. 



[In thousands of dollars] 

Fiscal year— 









Modification of convective clouds 

Research facilities center (prorated) 



1, 176 

1, 000 




2, 668 


Global monitoring for climatic change: 

Air quality analysis 



1, 563 

2, 138 





2, 298 

6, 334 

1, 146 

4, 577 


> From Federal Coordinating Council for Science, Engineering, and Technology. Interdepartmental Committee for Atmos- 
pheric Sciences. National Atmospheric Sciences Program: Fiscal Year 1978. ICAS 21-FY 78. August 1977, p. 89. 

NOAA 1 X-band Doppler radar operated by the Wave Propagation Laboratory 
of the National Oceanic and Atmospheric Administration. (Courtesy of the 
U.S. Department of Commerce.) 

The Florida Area Cumulus Experiment {FACE) 

The FACE program is conducted by the cumulus group of NO AA's 
National Hurricane and Experimental Meteorology Laboratory 


(NHEML) and is an outgrowth of a series of experiments in which 
individual clouds were seeded in Florida. These experiments demon- 
strated that dynamic seeding 90 is effective in increasing the sizes and 
lifetimes of individual cumulus clouds and the rainfall resulting from 
them. FACE is designed to determine whether dynamic seeding can 
be used to augment convective precipitation over a large area in south 
Florida by promoting the development of larger, better organized 
convective systems. Cloud merger, the joining of two formerly inde- 
pendent cloud entities, appears to be the important natural process 
leading to heavy and extensive rainfall in Florida. 91 

The design of FACE was intended to investigate two sequential 
questions. The first question was whether dynamic seeding can be used 
systematically to induce cloud merger and increase rainfall from the 
groups of subject clouds, and the second was to determine whether 
dynamic seeding can be used to produce a net increase in rainfall 
over a fixed target area. An affirmative answer to the first question, 
while necessary, may not be a sufficient condition to verify the second. 92 
FACE has been an exploratory experiment intended to answer these 
questions; hence, its design has been evolutionary. It cannot, there- 
fore, be regarded as a conclusive experiment, in spite of strong indica- 
tions of a positive seeding effect, it must be replicated with 
a predetermined design to confirm results achieved to date. It is 
planned that such a confirmatory FACE effort will begin in Florida 
during the summer of 1978. 93 

The experimental design for FACE is a random design, where the 
days over a single target are randomized into seeded and nonseeded 
days, with nonseeded days as the control. Experi